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28 Jul 2010

Volume 133, Issue 4, Articles (04xxxx)

Issue Cover Spotlight Figure

J. Chem. Phys. 133, 044901 (2010); doi:10.1063/1.3436517 (11 page)

Ian M. Craig, Christopher J. Tassone, Sarah H. Tolbert, and Benjamin J. Schwartz
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Communication: High-frequency acoustic excitations and boson peak in glasses: A study of their temperature dependence

B. Ruta, G. Baldi, V. M. Giordano, L. Orsingher, S. Rols, F. Scarponi, and G. Monaco

J. Chem. Phys. 133, 041101 (2010); doi:10.1063/1.3460815 (4 pages)

Online Publication Date: 27 July 2010

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The results of a combined experimental study of the high-frequency acoustic dynamics and of the vibrational density of states (VDOS) as a function of temperature in a glass of sorbitol are reported here. The excess in the VDOS at ∼ 4.5 meV over the Debye, elastic continuum prediction (boson peak) is found to be clearly related to anomalies observed in the acoustic dispersion curve in the mesoscopic wavenumber range of few nm−1. The quasiharmonic temperature dependence of the acoustic dispersion curves offers a natural explanation for the observed scaling of the boson peak with the elastic medium properties.
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62.65.+k Acoustical properties of solids
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
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Communication: Electric properties of the ThO(X 1Σ+) molecule

Alexei A. Buchachenko

J. Chem. Phys. 133, 041102 (2010); doi:10.1063/1.3459888 (3 pages)

Online Publication Date: 29 July 2010

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To assist the proposed search for the electric dipole moment of the electron with the thorium oxide, converged ab initio coupled cluster calculations are performed on the interaction energy, dipole moment, anisotropic static dipole polarizability, and quadrupole moment of the ThO(X 1Σ+) molecule as functions of internuclear distance. The rovibrational energy levels and wave functions are computed to derive the spectroscopic constants and matrix elements of electric properties. Ab initio calculations provide good agreement with the measured spectroscopic constants but call for a revision of the dissociation energy estimates from mass-spectrometric measurements and previous calculations.
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31.15.A- Ab initio calculations
31.15.bw Coupled-cluster theory
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.15.Fm Bond strengths, dissociation energies
33.15.Ta Mass spectra
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Insights into the orbital invariance problem in state-specific multireference coupled cluster theory

Francesco A. Evangelista and Jürgen Gauss

J. Chem. Phys. 133, 044101 (2010); doi:10.1063/1.3456546 (5 pages)

Online Publication Date: 22 July 2010

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In this communication we report the results of our studies on the orbital invariance properties of the state-specific multireference coupled cluster approach suggested by Mukherjee and co-workers (Mk-MRCC). In particular, we have gathered numerical evidence to show that even when the linear excitation manifold is modified in order to span the same space for each reference, the resulting method is not orbital invariant. In order to test this conjecture we have proposed a new truncation scheme (Mk-MRCCSDtq) which, in addition to full single and double excitations, contains partial triple and quadruple excitations. For a reference space generated by all possible combinations of two electrons in two orbitals, the linear excitation manifold of Mk-MRCCSDtq spans the same set for each reference determinant. Mk-MRCCSDtq is found to lack energy invariance for rotations among active molecular orbitals but it is less sensitive to orbital rotations than the conventional scheme which includes only singles and doubles (Mk-MRCCSD). Nevertheless, Mk-MRCCSDtq is a very accurate method, superior with respect to multireference configuration interaction approaches, and competitive with the active-space coupled cluster method and the MRexpT ansatz.
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31.15.bw Coupled-cluster theory

An efficient density-functional-theory force evaluation for large molecular systems

Simen Reine, Andreas Krapp, Maria Francesca Iozzi, Vebjørn Bakken, Trygve Helgaker, Filip Pawłowski, and Pawel Sałek

J. Chem. Phys. 133, 044102 (2010); doi:10.1063/1.3459061 (9 pages)

Online Publication Date: 22 July 2010

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An efficient, linear-scaling implementation of Kohn–Sham density-functional theory for the calculation of molecular forces for systems containing hundreds of atoms is presented. The density-fitted Coulomb force contribution is calculated in linear time by combining atomic integral screening with the continuous fast multipole method. For higher efficiency and greater simplicity, the near-field Coulomb force contribution is calculated by expanding the solid-harmonic Gaussian basis functions in Hermite rather than Cartesian Gaussians. The efficiency and linear complexity of the molecular-force evaluation is demonstrated by sample calculations and applied to the geometry optimization of a few selected large systems.
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31.15.E- Density-functional theory
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions
33.15.Mt Rotation, vibration, and vibration-rotation constants
31.15.-p Calculations and mathematical techniques in atomic and molecular physics

Ab initio statistical mechanics of surface adsorption and desorption. II. Nuclear quantum effects

D. Alfè and M. J. Gillan

J. Chem. Phys. 133, 044103 (2010); doi:10.1063/1.3466919 (9 pages)

Online Publication Date: 22 July 2010

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We show how the path-integral formulation of quantum statistical mechanics can be used to construct practical ab initio techniques for computing the chemical potential of molecules adsorbed on surfaces, with full inclusion of quantum nuclear effects. The techniques we describe are based on the computation of the potential of mean force on a chosen molecule and generalize the techniques developed recently for classical nuclei. We present practical calculations based on density functional theory with a generalized-gradient exchange-correlation functional for the case of H2O on the MgO (001) surface at low coverage. We note that the very high vibrational frequencies of the H2O molecule would normally require very large numbers of time slices (beads) in path-integral calculations, but we show that this requirement can be dramatically reduced by employing the idea of thermodynamic integration with respect to the number of beads. The validity and correctness of our path-integral calculations on the H2O/MgO(001) system are demonstrated by supporting calculations on a set of simple model systems for which quantum contributions to the free energy are known exactly from analytic arguments.
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68.43.Mn Adsorption kinetics
68.43.Nr Desorption kinetics
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
05.30.-d Quantum statistical mechanics
61.72.Qq Microscopic defects (voids, inclusions, etc.)

Accurate calculations of the hydration free energies of druglike molecules using the reference interaction site model

David S. Palmer, Volodymyr P. Sergiievskyi, Frank Jensen, and Maxim V. Fedorov

J. Chem. Phys. 133, 044104 (2010); doi:10.1063/1.3458798 (11 page)

Online Publication Date: 22 July 2010

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We report on the results of testing the reference interaction site model (RISM) for the estimation of the hydration free energy of druglike molecules. The optimum model was selected after testing of different RISM free energy expressions combined with different quantum mechanics and empirical force-field methods of structure optimization and atomic partial charge calculation. The final model gave a systematic error with a standard deviation of 2.6 kcal/mol for a test set of 31 molecules selected from the SAMPL1 blind challenge set [ J. P. Guthrie, J. Phys. Chem. B 113, 4501 (2009) ]. After parametrization of this model to include terms for the excluded volume and the number of atoms of different types in the molecule, the root mean squared error for a test set of 19 molecules was less than 1.2 kcal/mol.
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87.15.np Dissolution
87.15.ag Quantum calculations
82.39.Rt Reactions in complex biological systems

A multistage ab initio quantum wavepacket dynamics formalism for electronic structure and dynamics in open systems

Alexander B. Pacheco and Srinivasan S. Iyengar

J. Chem. Phys. 133, 044105 (2010); doi:10.1063/1.3463798 (15 pages)

Online Publication Date: 22 July 2010

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We propose a multistage quantum wavepacket dynamical treatment for the study of delocalized electronic systems as well as electron transport through donor-bridge-acceptor systems such as those found in molecular-wire/electrode networks. The full donor-bridge-acceptor system is treated through a rigorous partitioning scheme that utilizes judiciously placed offsetting absorbing and emitting boundary conditions. These facilitate a computationally efficient and potentially accurate treatment of the long-range coupling interactions between the bridge and donor/acceptor systems and the associated open system boundary conditions. Time-independent forms of the associated, partitioned equations are also derived. In the time-independent form corresponding to the bridge system, coupling to donor and acceptor, that is long-range interactions, is completely accounted. For the time-dependent study, the quantum dynamics of the electronic flux through the bridge-donor/acceptor interface is constructed using an accurate and efficient representation of the discretized quantum-mechanical free-propagator. A model for an electrode-molecular wire-electrode system is used to test the accuracy of the scheme proposed. Transmission probability is obtained directly from the probability density of the electronic flux in the acceptor region. Conductivity through the molecular wire is computed using a wavepacket flux correlation function.
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71.15.-m Methods of electronic structure calculations

Determination of spin Hamiltonians from projected single reference configuration interaction calculations. I. Spin 1/2 systems

A. Monari, D. Maynau, and J.-P. Malrieu

J. Chem. Phys. 133, 044106 (2010); doi:10.1063/1.3458642 (11 page)

Online Publication Date: 22 July 2010

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The most reliable wave-function based treatments of magnetic systems usually start from a complete active space self-consistent field calculation of the magnetic electrons in the magnetic orbitals, followed by extensive and expensive configuration interaction (CI) calculations. This second step, which introduces crucial spin polarization and dynamic correlation effects, is necessary to reach reliable values of the magnetic coupling constants. The computational cost of these approaches increases exponentially with the number of unpaired electrons. The single-determinantal unrestricted density functional Kohn–Sham calculations are computationally much simpler, and may provide reasonable estimates of these quantities, but their results are strongly dependent on the chosen exchange-correlation potential. The present work, which may be seen as an ab initio transcription of the unrestricted density functional theory technique, returns to the perturbative definition of the Heisenberg Hamiltonian as an effective Hamiltonian, and proposes a direct estimate of its diagonal energies through single reference CI calculations. The differences between these diagonal terms actually determine the entire Heisenberg Hamiltonian. The reference determinants must be vectors of the model space and the components on the other vectors of the model space are cancelled along the iterative process. The method is successfully tested on a series of bicentric and multicentric spin ½ systems. The projected single reference difference dedicated CI treatment is both accurate and of moderate cost. It opens the way to parameter-free calculations of large spin assemblies.
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75.10.Dg Crystal-field theory and spin Hamiltonians
75.10.Jm Quantized spin models, including quantum spin frustration
75.25.Dk Orbital, charge, and other orders, including coupling of these orders
75.50.Xx Molecular magnets

Embedding theory for excited states

Yuriy G. Khait and Mark R. Hoffmann

J. Chem. Phys. 133, 044107 (2010); doi:10.1063/1.3460594 (6 pages)

Online Publication Date: 22 July 2010

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Using the technique of Perdew and Levy [Phys. Rev. B 31, 6264 (1985)] , it is shown that both the density function theory (DFT)-in-DFT and wave function theory (WFT)-in-DFT embedding approaches are formally correct in studying not only the ground state but also a subset of the excited states of the total system. Without further approximations, the DFT-in-DFT embedding approach results in a pair of coupled Euler–Lagrange equations. In contrast to DFT-in-DFT, the WFT-in-DFT approach is shown to ensure a systematic description of excited states if such states are mainly related to excitations within the embedded subsystem. Possible ways for the practical realization of the WFT-in-DFT approach for studying excited states are briefly discussed.
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31.15.E- Density-functional theory
31.15.vj Electron correlation calculations for atoms and ions: excited states

A computational study of ultrafast acid dissociation and acid-base neutralization reactions. I. The model

Patrick Maurer, Vibin Thomas, Ugo Rivard, and Radu Iftimie

J. Chem. Phys. 133, 044108 (2010); doi:10.1063/1.3461162 (11 page)

Online Publication Date: 23 July 2010

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Ultrafast, time-resolved investigations of acid-base neutralization reactions have recently been performed using systems containing the photoacid 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (HPTS) and various Brønsted bases. Two conflicting neutralization mechanisms have been formulated by Mohammed et al. [Science 310, 83 (2005)] and Siwick et al. [J. Am. Chem. Soc. 129, 13412 (2007)] for the same acid-base system. Herein an ab initio molecular dynamics based computational model is formulated, which is able to investigate the validity of the proposed mechanisms in the general context of ground-state acid-base neutralization reactions. Our approach consists of using 2,4,6-tricyanophenol (exp. pKa ≅ 1) as a model for excited-state HPTS∗ (pKa ≅ 1.4) and carboxylate ions for the accepting base. We employ our recently proposed dipole-field/quantum mechanics (QM) treatment [ P. Maurer and R. Iftimie, J. Chem. Phys. 132, 074112 (2010) ] of the proton donor and acceptor molecules. This approach allows one to tune the free energy of neutralization to any desired value as well as model initial nonequilibrium hydration effects caused by a sudden increase in acidity, making it possible to achieve a more realistic comparison with experimental data than could be obtained via a full-QM treatment of the entire system. It is demonstrated that the dipole-field/QM model reproduces correctly key properties of the 2,4,6-tricyanophenol acid molecule including gas-phase proton dissociation energies and dipole moments, and condensed-phase hydration structure and pKa values.
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82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
33.15.Fm Bond strengths, dissociation energies
82.20.-w Chemical kinetics and dynamics
31.15.A- Ab initio calculations
31.50.Df Potential energy surfaces for excited electronic states
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
33.15.Bh General molecular conformation and symmetry; stereochemistry

Analyzing molecular static linear response properties with perturbed localized orbitals

Jochen Autschbach and Harry F. King

J. Chem. Phys. 133, 044109 (2010); doi:10.1063/1.3455709 (10 pages)

Online Publication Date: 23 July 2010

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Perturbed localized molecular orbitals (LMOs), correct to first order in an applied static perturbation and consistent with a chosen localization functional, are calculated using analytic derivative techniques. The formalism is outlined for a general static perturbation and variational localization functionals. Iterative and (formally) single-step approaches are compared. The implementation employs an iterative sequence of 2×2 orbital rotations. The procedure is verified by calculations of molecular electric-field perturbations. Boys LMO contributions to the electronic static polarizability and the electric-field perturbation of the 〈r2〉 expectation value are calculated and analyzed for ethene, ethyne, and fluoroethene (H2CCHF). For ethene, a comparison is made with results from a Pipek–Mezey localization. The calculations show that a chemically intuitive decomposition of the calculated properties is possible with the help of the LMO contributions and that the polarizability contributions in similar molecules are approximately transferable.
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31.15.am Relativistic configuration interaction (CI) and many-body perturbation calculations
31.15.ap Polarizabilities and other atomic and molecular properties
31.15.xt Variational techniques
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility

Solid-liquid surface free energy of Lennard-Jones liquid on smooth and rough surfaces computed by molecular dynamics using the phantom-wall method

Frédéric Leroy and Florian Müller-Plathe

J. Chem. Phys. 133, 044110 (2010); doi:10.1063/1.3458796 (11 page)

Online Publication Date: 23 July 2010

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Different model Lennard-Jones solid-liquid interfaces have been considered. In the systems, either the interaction strength between solid and liquid was varied, or the topography of the solid surface was modified. In all situations, the solid-liquid interfacial free energy variations with respect to a reference solid-liquid interface were quantified by means of a thermodynamic integration method [ F. Leroy et al., Macromol. Rapid Commun. 30, 864 (2009) ], referred to as the phantom-wall method. Additionally, the liquid-vapor surface free energy was determined. This result was combined with Young’s equation for contact angle calculations of cylindrical liquid droplets. It allowed us to show that the change in contact angle of a droplet placed on smooth solid surfaces with respect to solid-liquid interaction strength could be obtained by neglecting the solid-vapor surface free energy contribution when the solid-liquid interaction was weak. We also showed that the implementation of roughness by means of parallel grooves whose the density was varied could yield either higher or lower solid-liquid surface free energy, depending on the solid-liquid surface free energy of the smooth interface. Roughness led to lower surface free energy when the smooth surface had favorable interaction with the liquid, while it led to a higher surface free energy when the smooth surface had loose interactions with the liquid, though the effect was found to be weak. The consistency of the whole set of results, as well as agreement with the existing results on similar systems, shows the ability of the thermodynamic integration method employed here to capture the variation of interfacial thermodynamic quantities when modifying either the chemical nature or the topography of a solid surface in contact with a given liquid phase.
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68.03.Cd Surface tension and related phenomena
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
65.20.-w Thermal properties of liquids
68.35.Md Surface thermodynamics, surface energies

Multi-Jastrow trial wavefunctions for electronic structure calculations with quantum Monte Carlo

Thomas Bouabça, Benoît Braïda, and Michel Caffarel

J. Chem. Phys. 133, 044111 (2010); doi:10.1063/1.3457364 (18 pages)

Online Publication Date: 23 July 2010

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A new type of electronic trial wavefunction suitable for quantum Monte Carlo calculations of molecular systems is presented. In contrast with the standard Jastrow–Slater form built with a unique global Jastrow term, it is proposed to introduce individual Jastrow factors attached to molecular orbitals. Such a form is expected to be more physical since it allows to describe differently the local electronic correlations associated with various molecular environments (1s-core orbitals, 3d-magnetic orbitals, localized two-center σ-orbitals, delocalized π-orbitals, atomic lone pairs, etc.). In contrast with the standard form, introducing different Jastrow terms allows us to change the nodal structure of the wavefunction, a point which is important in the context of building better nodes for more accurate fixed-node diffusion Monte Carlo (FN-DMC) calculations. Another important aspect resulting from the use of local Jastrow terms is the possibility of defining and preoptimizing local and transferable correlated units for building complex trial wavefunctions from simple parts. The practical aspects associated with the computation of the intricate derivatives of the multi-Jastrow trial function are presented in detail. Some first illustrative applications for atoms of increasing size (O, S, and Cu) and for the potential energy curve and spectroscopic constants of the FH molecule are presented. In the case of the copper atom, the use of the multi-Jastrow form at the variational Monte Carlo level has allowed us to improve significantly the value of the total ground-state energy (about 75% of the correlation energy with only one determinant and three atomic orbital Jastrow factors). In the case of the FH molecule (fluorine hydride), it has been found that the multi-Jastrow nodes lead to an almost exact FN-DMC value of the dissociation energy [D0 = −140.7(4) kcal/mol instead of the estimated nonrelativistic Born–Oppenheimer exact value of −141.1], which is not the case with standard nodes, D0 = −138.3(4) kcal/mol.
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31.15.-p Calculations and mathematical techniques in atomic and molecular physics
31.50.-x Potential energy surfaces

Fluctuating dynamics of nematic liquid crystals using the stochastic method of lines

A. K. Bhattacharjee, Gautam I. Menon, and R. Adhikari

J. Chem. Phys. 133, 044112 (2010); doi:10.1063/1.3455206 (6 pages)

Online Publication Date: 27 July 2010

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We construct Langevin equations describing the fluctuations of the tensor order parameter Qαβ in nematic liquid crystals by adding noise terms to time-dependent variational equations that follow from the Ginzburg–Landau–de Gennes free energy. The noise is required to preserve the symmetry and tracelessness of the tensor order parameter and must satisfy a fluctuation-dissipation relation at thermal equilibrium. We construct a noise with these properties in a basis of symmetric traceless matrices and show that the Langevin equations can be solved numerically in this basis using a stochastic version of the method of lines. The numerical method is validated by comparing equilibrium probability distributions, structure factors, and dynamic correlations obtained from these numerical solutions with analytic predictions. We demonstrate excellent agreement between numerics and theory. This methodology can be applied to the study of phenomena where fluctuations in both the magnitude and direction of nematic order are important, as for instance, in the nematic swarms which produce enhanced opalescence near the isotropic-nematic transition or the problem of nucleation of the nematic from the isotropic phase.
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61.30.Jf Defects in liquid crystals
64.60.Q- Nucleation
05.40.Ca Noise
64.70.M- Transitions in liquid crystals
02.50.Ey Stochastic processes

Electronic excitation energy calculation by the fragment molecular orbital method with three-body effects

Mahito Chiba and Tetsuya Koido

J. Chem. Phys. 133, 044113 (2010); doi:10.1063/1.3462247 (6 pages)

Online Publication Date: 27 July 2010

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A scheme for full quantum electronic excited state calculation is proposed that is based on the fragment molecular orbital (FMO) method with three-body effects. The accuracy and efficiency of this scheme is checked by calculating the excitation energy of hydrated formaldehyde and hydrated phenol. In all cases, three-body effects improved the excitation energy by the one- and two-body FMO methods with small computational cost, and the excitation energy approached more closely the full calculation value. The results also show that the three-body effects were relatively large and cannot be neglected.
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31.15.vj Electron correlation calculations for atoms and ions: excited states
31.50.Df Potential energy surfaces for excited electronic states
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
31.15.-p Calculations and mathematical techniques in atomic and molecular physics

Free energy calculation using molecular dynamics simulation combined with the three dimensional reference interaction site model theory. I. Free energy perturbation and thermodynamic integration along a coupling parameter

Tatsuhiko Miyata, Yasuhiro Ikuta, and Fumio Hirata

J. Chem. Phys. 133, 044114 (2010); doi:10.1063/1.3462276 (15 pages)

Online Publication Date: 28 July 2010

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This article proposes a free energy calculation method based on the molecular dynamics simulation combined with the three dimensional reference interaction site model theory. This study employs the free energy perturbation (FEP) and the thermodynamic integration (TDI) along the coupling parameters to control the interaction potential. To illustrate the method, we applied it to a complex formation process in aqueous solutions between a crown ether molecule 18-Crown-6 (18C6) and a potassium ion as one of the simplest model systems. Two coupling parameters were introduced to switch the Lennard-Jones potential and the Coulomb potential separately. We tested two coupling procedures: one is a “sequential-coupling” to couple the Lennard-Jones interaction followed by the Coulomb coupling, and the other is a “mixed-coupling” to couple both the Lennard-Jones and the Coulomb interactions together as much as possible. The sequential-coupling both for FEP and TDI turned out to be accurate and easily handled since it was numerically well-behaved. Furthermore, it was found that the sequential-coupling had relatively small statistical errors. TDI along the mixed-coupling integral path was to be carried out carefully, paying attention to a numerical behavior of the integrand. The present model system exhibited a nonmonotonic behavior in the integrands for TDI along the mixed-coupling integral path and also showed a relatively large statistical error. A coincidence within a statistical error was obtained among the results of the free energy differences evaluated by FEP, TDI with the sequential-coupling, and TDI with the mixed-coupling. The last one is most attractive in terms of the computer power and is accurate enough if one uses a proper set of windows, taking the numerical behavior of the integrands into account. TDI along the sequential-coupling integral path would be the most convenient among the methods we tested, since it seemed to be well-balanced between the computational load and the accuracy. The numerical results reported in this article qualitatively agree with the experimental data for the potassium ion recognition by the 18C6 in aqueous solution.
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05.70.Ce Thermodynamic functions and equations of state
61.25.Em Molecular liquids
61.20.Ja Computer simulation of liquid structure

An efficient umbrella potential for the accurate calculation of free energies by molecular simulation

Di Wu

J. Chem. Phys. 133, 044115 (2010); doi:10.1063/1.3464330 (9 pages)

Online Publication Date: 29 July 2010

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Umbrella sampling has been widely used to calculate free energies in many chemical and biological applications because it can effectively bridge the systems of interest and sample in the united phase space that is essential to yield accurate results. Many algorithms have implemented the idea of umbrella sampling that greatly improves the calculation of free energies. An efficient umbrella potential not only can connect the systems of interest, but also can lower the energetic barriers and facilitate the sampling over the relevant phase spaces. Here we present such an umbrella potential that is built on the equations of the weighted histogram analysis method. The proposed umbrella potential can facilitate the sampling of the important phase spaces of the systems of interest, which ensures the accurate calculation of free energies. We test this umbrella potential using a harmonic-model system, a water system, and a Lennard-Jones system. We demonstrate that this umbrella potential is effective in the circumstances when the systems of interest do not exhibit overlap in their phase spaces.
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05.70.Ce Thermodynamic functions and equations of state
31.10.+z Theory of electronic structure, electronic transitions, and chemical binding
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions

Hartree–Fock perturbative corrections for total and reaction energies

Jia Deng, Andrew T. B. Gilbert, and Peter M. W. Gill

J. Chem. Phys. 133, 044116 (2010); doi:10.1063/1.3463800 (6 pages)

Online Publication Date: 30 July 2010

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We have performed an assessment of the Hartree–Fock perturbative correction (HFPC) on a large and diverse set of molecules and reactions. Errors in both absolute and reaction energies with respect to converged secondary basis Hartree–Fock results are reported for a wide spectrum of primary/secondary basis set combinations. These results show that using an adequate primary basis, HFPC can accurately reproduce secondary basis energies at a substantially reduced cost. Comparisons of HFPC with the related dual basis Hartree–Fock (DBHF) scheme are also made for several molecules and target secondary basis sets. Our results indicate that HFPC is faster and more accurate than DBHF for approaching triple-ζ basis sets. For quadruple-ζ secondary basis sets, HFPC is capable of yielding more accurate energies at a marginally increased cost over DBHF.
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31.15.xr Self-consistent-field methods
82.20.-w Chemical kinetics and dynamics
31.15.xp Perturbation theory

Transferability of anharmonic force fields in simulations of molecular vibrations

Václav Parchaňský and Petr Bouř

J. Chem. Phys. 133, 044117 (2010); doi:10.1063/1.3464759 (10 pages)

Online Publication Date: 30 July 2010

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Accurate simulations of vibrational molecular spectra require precise molecular force fields, at least with cubic and quartic anharmonic corrections beyond the harmonic limits. Generation of such force field terms becomes computationally prohibitive for larger molecules. In this work, an alternate possibility is explored, where approximate anharmonic force field components are obtained from molecular fragments. Transferability properties of the cubic and incomplete quartic fields are discussed and tested on model oligoproline molecules. Automatic transfer schemes including cubic, two and three atomic quartic force constants are developed and implemented. The results indicate that the main vibrational interactions in molecules are local and the anharmonic constants are mostly well amendable to the transfer. Exact anharmonic normal mode force fields of larger molecules compared very well to those obtained from smaller molecular parts. The most important changes in vibrational spectra caused by the anharmonic interactions could be reproduced with two and three atomic force field terms. The transfer scheme thus provides molecular anharmonic force fields without a significant loss of accuracy and brings significant savings of computer time and memory needed to generate molecular vibrational energies and spectra.
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33.20.Tp Vibrational analysis
31.15.-p Calculations and mathematical techniques in atomic and molecular physics
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

Dissociation energy of the ground state of NaH

Hsien-Yu Huang, Tsai-Lien Lu, Thou-Jen Whang, Yung-Yung Chang, and Chin-Chun Tsai

J. Chem. Phys. 133, 044301 (2010); doi:10.1063/1.3458914 (7 pages)

Online Publication Date: 22 July 2010

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The dissociation energy of the ground state of NaH was determined by analyzing the observed near dissociation rovibrational levels. These levels were reached by stimulated emission pumping and fluorescence depletion spectroscopy. A total of 114 rovibrational levels in the ranges 9 ≤ v″ ≤ 21 and 1 ≤ J″ ≤ 14 were assigned to the X 1Σ+ state of NaH. The highest vibrational level observed was only about 40 cm−1 from the dissociation limit in the ground state. One quasibound state, above the dissociation limit and confined by the centrifugal barrier, was observed. Determining the vibrational quantum number at dissociation vD from the highest four vibrational levels yielded the dissociation energy De = 15 815±5 cm−1. Based on new observations and available data, a set of Dunham coefficients and the rotationless Rydberg–Klein–Rees curve were constructed. The effective potential curve and the quasibound states were discussed.
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33.15.Fm Bond strengths, dissociation energies
33.20.Vq Vibration-rotation analysis
33.80.Be Level crossing and optical pumping
33.20.Tp Vibrational analysis
33.80.Gj Diffuse spectra; predissociation, photodissociation
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
31.50.Df Potential energy surfaces for excited electronic states
03.65.Ge Solutions of wave equations: bound states

Fivefold differential cross sections for ground-state ionization of aligned H2 by electron impact

Arne Senftleben, Ola Al-Hagan, Thomas Pflüger, Xueguang Ren, Don Madison, Alexander Dorn, and Joachim Ullrich

J. Chem. Phys. 133, 044302 (2010); doi:10.1063/1.3457155 (7 pages)

Online Publication Date: 22 July 2010

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We discuss the ionization of aligned hydrogen molecules into their ionic ground state by 200 eV electrons. Using a reaction microscope, the complete electron scattering kinematics is imaged over a large solid angle. Simultaneously, the molecular alignment is derived from postcollision dissociation of the residual ion. It is found that the ionization cross section is maximized for small angles between the internuclear axis and the momentum transfer. Fivefold differential cross sections (5DCSs) reveal subtle differences in the scattering process for the distinct alignments. We compare our observations with theoretical 5DCSs obtained with an adapted molecular three-body distorted wave model that reproduces most of the results, although discrepancies remain.
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34.80.Gs Molecular excitation and ionization

Vibrationally resolved photoelectron imaging of gold hydride cluster anions: AuH− and Au2H−

Xia Wu, Zhengbo Qin, Hua Xie, Ran Cong, Xiaohu Wu, Zichao Tang, and Hongjun Fan

J. Chem. Phys. 133, 044303 (2010); doi:10.1063/1.3456373 (5 pages)

Online Publication Date: 23 July 2010

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Photoelectron spectra and angular distributions in photodetachment of gold hydride anions AuH− and Au2H− have been obtained using photoelectron velocity-map imaging. Both the images exhibit vibrationally resolved ground state transitions. The adiabatic electron affinities of AuH and Au2H are measured to be 0.758(20) and 3.437(3) eV, respectively. Franck–Condon analyses of the AuH spectra determined that the equilibrium bond length of the ground state of AuH− is 1.597(6) math. The photoelectron images of Au2H− show a vibrational progression of 148(4) cm−1 assigned to the Au–Au stretching mode at the ground state. Ab initio calculation results are in excellent agreement with the experimental results. For the ground state of Au2H, a new bent Au–Au–H structure with the angle of 131° is suggested. Moreover, energy-dependent photoelectron anisotropy parameters are also reported and discussed.
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36.40.Mr Spectroscopy and geometrical structure of clusters
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.80.Eh Autoionization, photoionization, and photodetachment
33.60.+q Photoelectron spectra
33.15.Dj Interatomic distances and angles
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
31.15.A- Ab initio calculations
36.40.Wa Charged clusters

Sound-driven fluid dynamics in pressurized carbon dioxide

Maikel M. van Iersel, Robert Mettin, Nieck E. Benes, Dirk Schwarzer, and Jos T. F. Keurentjes

J. Chem. Phys. 133, 044304 (2010); doi:10.1063/1.3463444 (4 pages)

Online Publication Date: 23 July 2010

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Using high-speed visualization we demonstrate that ultrasound irradiation of pressurized carbon dioxide (CO2) induces phenomena that do not occur in ordinary liquids at ambient conditions. For a near-critical mixture of CO2 and argon, sonication leads to extremely fast local phase separation, in which the system enters and leaves the two-phase region with the frequency of the imposed sound field. This phase transition can propagate with the speed of sound, but can also be located at fixed positions in the case of a standing sound wave. Sonication of a vapor-liquid interface creates a fine dispersion of liquid and vapor, irrespective whether the ultrasound horn is placed in the liquid or the vapor phase. In the absence of an interface, sonication of the liquid leads to ejection of a macroscopic vapor phase from the ultrasound horn with a velocity of several meters per second in the direction of wave propagation. The findings reported here potentially provide a tunable and noninvasive means for enhancing mass and heat transfer in high-pressure fluids.
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62.60.+v Acoustical properties of liquids
64.70.F- Liquid-vapor transitions
62.50.-p High-pressure effects in solids and liquids

Use of complex configuration interaction calculations and the stationary principle for the description of metastable electronic states of HCl−

Michael Honigmann, Heinz-Peter Liebermann, and Robert J. Buenker

J. Chem. Phys. 133, 044305 (2010); doi:10.1063/1.3467885 (15 pages)

Online Publication Date: 26 July 2010

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The complex multireference single- and double-excitation configuration interaction method has been employed to compute potential curves for the anion of the hydrogen chloride molecule. First, conventional CI calculations with real basis functions have been carried out to determine the potential curves of both HCl and its anion over a large range of internuclear distance. It is shown that adding basis functions with very small exponents leads to sharply avoided crossings for the HCl− potentials that greatly complicate the search for resonance states thought to be responsible for features observed in electron collision experiments. By limiting the number of such diffuse-type functions it is possible to describe resonance states at a highly correlated level and still account for their interaction with the continuum in which they are embedded. In the present study of the HCl− anion the complex basis function technique of Moiseyev–Corcoran and McCurdy–Resigno is employed to calculate the energy positions and line-widths of the resonance states. Two states of 2Σ+ symmetry are calculated which have potentials that have significantly different shapes than that of the neutral ground state and thus contribute to the cross section for vibrational excitation of the neutral HCl molecule induced by low-energy electron collisions. The lower of these (1 2Σ+) correlates smoothly with the bound anionic ground state at large internuclear distances and is seen to be responsible for the sharp peaks observed in the low-energy region of the spectrum. The upper state (3 2Σ+) has a much larger bond length and is assigned to the broad bands observed with a maximum in the 2.5–3.0 eV range. The present calculations thus stand in contradiction to earlier claims that the above peaks are caused by so-called virtual states without a definite autoionization lifetime.
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31.15.am Relativistic configuration interaction (CI) and many-body perturbation calculations
31.15.vj Electron correlation calculations for atoms and ions: excited states
34.80.Bm Elastic scattering
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.15.Dj Interatomic distances and angles

Structure and spectroscopy of ground and excited states of LiYb

P. Zhang, H. R. Sadeghpour, and A. Dalgarno

J. Chem. Phys. 133, 044306 (2010); doi:10.1063/1.3462245 (10 pages)

Online Publication Date: 28 July 2010

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Multireference configuration interaction and coupled cluster calculations have been carried out to determine the potential energy curves for the ground and low-lying excited states of the LiYb molecule. The scalar relativistic effects have been included by means of the Douglas–Kroll Hamiltonian and effective core potential and the spin-orbit couplings have been evaluated by the full microscopic Breit–Pauli operator. The LiYb permanent dipole moment, static dipole polarizability, and Franck–Condon factors have been determined. Perturbations of the vibrational spectrum due to nonadiabatic interactions are discussed.
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31.15.am Relativistic configuration interaction (CI) and many-body perturbation calculations
31.15.bw Coupled-cluster theory
31.50.Df Potential energy surfaces for excited electronic states
31.50.Bc Potential energy surfaces for ground electronic states
31.15.aj Relativistic corrections, spin-orbit effects, fine structure; hyperfine structure
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility

IR spectra of protonated benzaldehyde clusters, C7H7O+–Ln (L = Ar,N2;n ≤ 2): Ion-ligand binding motifs of the cis and trans oxonium isomers

Shamik Chakraborty, Alexander Patzer, and Otto Dopfer

J. Chem. Phys. 133, 044307 (2010); doi:10.1063/1.3460458 (12 pages)

Online Publication Date: 28 July 2010

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Infrared photodissociation (IRPD) spectra of mass-selected protonated benzaldehyde (C7H7O+,BZH+) and its weakly bound clusters with Ar and N2 produced in an electron impact source are recorded in the C–H and O–H stretch ranges. The experimental results are supported by ab initio and density functional calculations. Analysis of the IRPD spectrum of the BZH+ monomer is consistent with the presence of the cis and trans isomers of the oxonium ions, which is confirmed by the cluster spectra. No signature of the less stable carbenium ions is detected. Frequency shifts in the IRPD spectra of dimers and trimers provide information about the preferred intermolecular ligand binding site (π-bonding versus H-bonding) and the corresponding interaction strength. H-bonding to the OH group of the oxonium ions of BZH+ is found to be favored over π-bonding to the aromatic ring for both Ar and N2. There are significant differences in the microsolvation structure and energetics of the cis and trans oxonium isomers of BZH+ due to the rather different acidities of their OH groups and isomer-dependent effects arising from steric hindrance. The large positive partial charge of the protonated formyl group implies that the cluster growth of the larger clusters continues by further solvation of the protonated substituent rather than the aromatic ring.
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36.40.Wa Charged clusters
36.40.Mr Spectroscopy and geometrical structure of clusters
31.15.A- Ab initio calculations
33.15.Fm Bond strengths, dissociation energies
33.20.Ea Infrared spectra
31.15.E- Density-functional theory

Cavity-enhanced resonant photoacoustic spectroscopy with optical feedback cw diode lasers: A novel technique for ultratrace gas analysis and high-resolution spectroscopy

Michael Hippler, Christian Mohr, Katherine A. Keen, and Edward D. McNaghten

J. Chem. Phys. 133, 044308 (2010); doi:10.1063/1.3461061 (8 pages)

Online Publication Date: 29 July 2010

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Cavity-enhanced resonant photoacoustic spectroscopy with optical feedback cw diode lasers (OF-CERPAS) is introduced as a novel technique for ultratrace gas analysis and high-resolution spectroscopy. In the scheme, a single-mode cw diode laser (3 mW, 635 nm) is coupled into a high-finesse linear cavity and stabilized to the cavity by optical feedback. Inside the cavity, a build-up of laser power to at least 2.5 W occurs. Absorbing gas phase species inside the cavity are detected with high sensitivity by the photoacoustic effect using a microphone embedded in the cavity. To increase sensitivity further, coupling into the cavity is modulated at a frequency corresponding to a longitudinal resonance of an organ pipe acoustic resonator (f = 1.35 kHz and Q ≈ 10). The technique has been characterized by measuring very weak water overtone transitions near 635 nm. Normalized noise-equivalent absorption coefficients are determined as α ≈ 4.4×10−9 cm−1 s1/2 (1 s integration time) and 2.6×10−11 cm−1 s1/2 W (1 s integration time and 1 W laser power). These sensitivities compare favorably with existing state-of-the-art techniques. As an advantage, OF-CERPAS is a “zero-background” method which increases selectivity and sensitivity, and its sensitivity scales with laser power.
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82.80.Kq Energy-conversion spectro-analytical methods (e.g., photoacoustic, photothermal, and optogalvanic spectroscopic methods)
43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Px Semiconductor lasers; laser diodes
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Ligand effect on uranium isotope fractionations caused by nuclear volume effects: An ab initio relativistic molecular orbital study

Minori Abe, Tatsuya Suzuki, Yasuhiko Fujii, Masahiko Hada, and Kimihiko Hirao

J. Chem. Phys. 133, 044309 (2010); doi:10.1063/1.3463797 (5 pages)

Online Publication Date: 30 July 2010

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We have calculated the nuclear volume term (ln Knv) of the isotope fractionation coefficient (ε) between 235U–238U isotope pairs by considering the effect of ligand coordination in a U(IV)–U(VI) reaction system. The reactants were modeled as [UO2Cl3]− and [UO2Cl4]2− for U(VI), and UCl4 for U(IV). We adopted the Dirac–Coulomb Hartree–Fock method with the Gaussian-type finite nucleus model. The result obtained was ln Knv = 0.001 90 at 308 K, while the experimentally estimated value of ln Knv is 0.002 24. We also discuss how the ligand affects the value of ln Knv, especially for the various structures of different compounds, and different ligands within the halogen ion series (F, Cl, and Br).
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31.15.-p Calculations and mathematical techniques in atomic and molecular physics
36.20.Hb Configuration (bonds, dimensions)
31.30.J- Relativistic and quantum electrodynamic (QED) effects in atoms, molecules, and ions
31.15.aj Relativistic corrections, spin-orbit effects, fine structure; hyperfine structure

Spectroscopic study of CHBrF2 up to 9500 cm−1: Vibrational analysis, integrated band intensities, and ab initio calculations

Andrea Pietropolli Charmet, Paolo Stoppa, Nicola Tasinato, Alessandro Baldan, Santi Giorgianni, and Alberto Gambi

J. Chem. Phys. 133, 044310 (2010); doi:10.1063/1.3460922 (10 pages)

Online Publication Date: 30 July 2010

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The gas-phase infrared spectra of bromodifluoromethane, CHBrF2, have been examined at medium resolution in the range of 200–9500 cm−1. The assignment of the absorptions in terms of fundamental, overtone, combination, and hot bands, assisted by quantum chemical calculations is consistent all over the region investigated. Accurate values of integrated band intensities have also been determined for the first time in the range of 500–6000 cm−1. Structural and molecular spectroscopic properties have been calculated at high level of theory. The coupled cluster CCSD(T) method in conjunction with a hierarchical series of correlation consistent basis sets has been employed and extrapolation to complete basis set has been considered for the equilibrium geometry. Vibrational analysis based on the second order perturbation theory has been carried out with the ab initio anharmonic force constants calculated using the second order Møller–Plesset perturbation as well as coupled cluster [CCSD(T)] theory. A good agreement between the computed and the experimental data also including the integrated infrared band intensities has been obtained.
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33.20.Ea Infrared spectra
33.20.Tp Vibrational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
31.15.A- Ab initio calculations
31.15.bw Coupled-cluster theory
31.15.xp Perturbation theory

Cross sections for rotational decoherence of perturbed nitrogen measured via decay of laser-induced alignment

N. Owschimikow, F. Königsmann, J. Maurer, P. Giese, A. Ott, B. Schmidt, and N. Schwentner

J. Chem. Phys. 133, 044311 (2010); doi:10.1063/1.3464487 (13 pages)

Online Publication Date: 30 July 2010

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We quantitatively determine cross sections for rotational decoherence from the decay of nonadiabatic laser-induced alignment in nitrogen and nitrogen-foreign gas mixtures in a temperature range between 80 K and room temperature. The cross section for rotational decoherence in pure nitrogen decreases from 102 Å2 at 80 K to 48 Å2 at 295 K, leading to long-lived coherences even at high temperatures. Comparison with the broadening of the transition lines of the Raman Q-branch reported in the literature shows that the decay of rotational coherence proceeds at the same rate as rotational depopulation. This is verified also for mixtures of nitrogen with hydrogen, helium, argon, and krypton. We discuss limits posed by a possible J-dependence of the cross sections and strategies for state resolved determination from the time-dependent alignment signal.
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33.20.Sn Rotational analysis
32.70.Cs Oscillator strengths, lifetimes, transition moments
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
32.30.-r Atomic spectra
33.20.Fb Raman and Rayleigh spectra (including optical scattering)
32.70.Jz Line shapes, widths, and shifts
33.70.Jg Line and band widths, shapes, and shifts

Finite temperature quantum statistics of H3+ molecular ion

Ilkka Kylänpää and Tapio T. Rantala

J. Chem. Phys. 133, 044312 (2010); doi:10.1063/1.3464758 (5 pages)

Online Publication Date: 30 July 2010

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Full quantum statistical NVT simulation of the five-particle system H3+ has been carried out using the path integral Monte Carlo method. Structure and energetics are evaluated as a function of temperature up to the thermal dissociation limit. The weakly density dependent dissociation temperature is found to be around 4000 K. Contributions from the quantum dynamics and thermal motion are sorted out by comparing differences between simulations with quantum and classical nuclei. The essential role of the quantum description of the protons is established.
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31.15.bt Statistical model calculations (including Thomas-Fermi and Thomas-Fermi-Dirac models)
33.15.Bh General molecular conformation and symmetry; stereochemistry
05.30.-d Quantum statistical mechanics
02.50.Ng Distribution theory and Monte Carlo studies

Comparisons of classical and Wigner sampling of transition state energy levels for quasiclassical trajectory chemical dynamics simulations

Lipeng Sun and William L. Hase

J. Chem. Phys. 133, 044313 (2010); doi:10.1063/1.3463717 (9 pages)

Online Publication Date: 30 July 2010

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Quasiclassical trajectory calculations are compared, with classical and Wigner sampling of transition state (TS) energy levels, for C2H5F ≠ →HF+C2H4 product energy partitioning and [Cl⋯CH3⋯Cl]− central barrier dynamics. The calculations with Wigner sampling are reported here for comparison with the previously reported calculations with classical sampling [ Y. J. Cho et al., J. Chem. Phys. 96, 8275 (1992) ; L. Sun and W. L. Hase, J. Chem. Phys. 121, 8831 (2004) ]. The C2H5F ≠ calculations were performed with direct dynamics at the MP2/6-31G∗ level of theory. Classical and Wigner sampling give post-transition state dynamics, for these two chemical systems, which are the same within statistical uncertainties. This is a result of important equivalences in these two sampling methods for selecting initial conditions at a TS. In contrast, classical and Wigner sampling often give different photodissociation dynamics [ R. Schinke, J. Phys. Chem. 92, 3195 (1988) ]. Here the sampling is performed for a vibrational state of the ground electronic state potential energy surface (PES), which is then projected onto the excited electronic state’s PES. Differences between the ground and the excited PESs may give rise to substantially different excitations of the vibrational and dissociative coordinates on the excited state PES by classical and Wigner sampling, resulting in different photodissociation dynamics.
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82.20.Db Transition state theory and statistical theories of rate constants
82.50.-m Photochemistry
82.20.Kh Potential energy surfaces for chemical reactions
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.80.Gj Diffuse spectra; predissociation, photodissociation
back to top Condensed Phase Dynamics, Structure, and Thermodynamics: Spectroscopy, Reactions, and Relaxation

Microscopic dynamics of supercooled low weight alcohols

Ricardo Palomar and Gemma Sesé

J. Chem. Phys. 133, 044501 (2010); doi:10.1063/1.3466749 (7 pages)

Online Publication Date: 22 July 2010

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Dynamical properties of low weight alcohols have been analyzed both in the liquid and the supercooled states. Realistic interatomic potential models for methanol and ethanol have been used. The influence of temperature on the hydrogen-bonded structure has been undertaken. Remarkable similarities have been obtained in both systems. Velocity autocorrelation functions have been evaluated for molecules participating in zero, one, and two hydrogen bonds at a wide range of temperatures. A backscattering area preceded by a shoulder has been identified as a signature of this function when evaluated for the subset of molecules that participate in two hydrogen bonds. Memory functions have also been evaluated. Their initial decay depends only slightly upon temperature. A more marked temperature dependence is observed for the nonassociated molecules. For them, reasonable agreement with the mode-coupling approach predictions has been encountered.
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61.50.Lt Crystal binding; cohesive energy

Resummed thermodynamic perturbation theory for central force associating potential: One-patch model

Y. V. Kalyuzhnyi, H. Docherty, and P. T. Cummings

J. Chem. Phys. 133, 044502 (2010); doi:10.1063/1.3459098 (8 pages)

Online Publication Date: 22 July 2010

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A resummed thermodynamic perturbation theory for associating fluids with multiply bondable central force associating potential is proposed. We consider a simple one-patch model for associating fluids. The model is represented by the hard-sphere system with a circular attractive patch on the surface of each hard-sphere. Resummation is carried out to account for the blocking effects, i.e., when the bonding of a particle restricts (blocks) its ability to bond with other particles. Closed form analytical expressions for thermodynamical properties (Helmholtz free energy, pressure, internal energy, and chemical potential) of the model with a doubly bondable patch at all degrees of the blockage are presented. In the limiting case of total blockage, when the particles become only singly bondable, our theory reduces to Wertheim’s thermodynamic perturbation theory for dimerizing fluids. To validate the accuracy of the theory we compare to exact values, for the thermodynamical properties of the system, as determined by Monte Carlo computer simulations. In addition we compare the fraction of multiply bonded particles at different values of the density and temperature. Very good agreement between predictions of the theory, corrected for ring formation, and Monte Carlo computer simulation values was found in all cases studied. Less accurate are the original versions of the theory and Wertheim’s thermodynamic perturbation theory for dimerization, especially at lower temperatures and larger sizes of the attractive patch.
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05.70.Ce Thermodynamic functions and equations of state

Brillouin scattering study of liquid methane under high pressures and high temperatures

Min Li, Fangfei Li, Wei Gao, Chunli Ma, Liyin Huang, Qiang Zhou, and Qiliang Cui

J. Chem. Phys. 133, 044503 (2010); doi:10.1063/1.3449141 (7 pages)

Online Publication Date: 22 July 2010

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Brillouin scattering measurements were performed on liquid methane using diamond anvil cell along five isotherms and at the pressures up to solidification points. Sound velocity, refractive index, and adiabatic bulk modulus of liquid methane as function of pressure were determined with the measurements from the platelet and backscattering geometries. The maximum pressure and temperature reached up to 5.12 GPa and 539 K. The sound velocity, refractive index, and adiabatic bulk modulus increased with pressure along each isotherm. The equation of state of liquid methane was determined from the present Brillouin results.
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78.35.+c Brillouin and Rayleigh scattering; other light scattering
62.50.-p High-pressure effects in solids and liquids
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
62.60.+v Acoustical properties of liquids

Exciton localization in disordered poly(3-hexylthiophene)

William Barford, David G. Lidzey, Dmitry V. Makhov, and Anthony J. H. Meijer

J. Chem. Phys. 133, 044504 (2010); doi:10.1063/1.3459099 (6 pages)

Online Publication Date: 22 July 2010

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Singlet exciton localization in conformationally disordered poly(3-hexylthiophene) (P3HT) is investigated via configuration interaction (singles) calculations of the Pariser–Parr–Pople model. The P3HT structures are generated by molecular dynamics simulations. The lowest-lying excitons are spatially localized, space filling, and nonoverlapping. These define spectroscopic segments or chromophores. The strong conformational disorder in P3HT causes breaks in the π-conjugation. Depending on the relative values of the disorder-induced localization length and the distances between the π-conjugation breaks, these breaks sometimes serve to pin the low-lying localized excitons. The exciton confinement also causes a local spectrum of low-lying exciton states. Coulomb-induced intra- or interchain interactions between spectroscopic segments in close spatial proximity can delocalize an exciton across these segments, in principle causing phase coherent transition dipole moments.
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71.35.-y Excitons and related phenomena

Effect of state-selective reactive decay on the evolution of quantum systems

A. I. Shushin

J. Chem. Phys. 133, 044505 (2010); doi:10.1063/1.3461133 (7 pages)

Online Publication Date: 22 July 2010

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The effect of state-selective reactive decay on the relaxation kinetics of quantum multistate systems is studied in detail in the Bloch–Redfield approach (BRA). The results are applied to the analysis of this effect in radical pair recombination kinetics. The BRA is shown to be able to describe quantitatively most important specific features of the recombination kinetics including those predicted by phenomenological treatment and by recently proposed approaches based on quantum measurement theories.
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03.65.Ta Foundations of quantum mechanics; measurement theory
82.30.Nr Association, addition, insertion, cluster formation
03.65.Sq Semiclassical theories and applications
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.20.-w Chemical kinetics and dynamics

Spatial averaging for small molecule diffusion in condensed phase environments

Nuria Plattner, J. D. Doll, and Markus Meuwly

J. Chem. Phys. 133, 044506 (2010); doi:10.1063/1.3458639 (10 pages)

Online Publication Date: 26 July 2010

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Spatial averaging is a new approach for sampling rare-event problems. The approach modifies the importance function which improves the sampling efficiency while keeping a defined relation to the original statistical distribution. In this work, spatial averaging is applied to multidimensional systems for typical problems arising in physical chemistry. They include (I) a CO molecule diffusing on an amorphous ice surface, (II) a hydrogen molecule probing favorable positions in amorphous ice, and (III) CO migration in myoglobin. The systems encompass a wide range of energy barriers and for all of them spatial averaging is found to outperform conventional Metropolis Monte Carlo. It is also found that optimal simulation parameters are surprisingly similar for the different systems studied, in particular, the radius of the point cloud over which the potential energy function is averaged. For H2 diffusing in amorphous ice it is found that facile migration is possible which is in agreement with previous suggestions from experiment. The free energy barriers involved are typically lower than 1 kcal/mol. Spatial averaging simulations for CO in myoglobin are able to locate all currently characterized metastable states. Overall, it is found that spatial averaging considerably improves the sampling of configurational space.
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87.15.ak Monte Carlo simulations
66.30.-h Diffusion in solids

An analysis of the NEXAFS spectra of a molecular crystal: α-glycine

Craig P. Schwartz, Richard J. Saykally, and David Prendergast

J. Chem. Phys. 133, 044507 (2010); doi:10.1063/1.3462243 (6 pages)

Online Publication Date: 27 July 2010

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The nitrogen K-edge near edge x-ray absorption fine structure spectrum of α-crystalline glycine has been calculated for temperatures ranging from 0 to 450 K. Significant temperature dependent spectral changes are predicted. The calculated room temperature spectrum is in good agreement with the experiment. At high temperatures, molecular motions strongly influence the spectrum, as any unique spectrum from an individual instantaneous configuration does not resemble the experimental result or the average calculated spectrum; complex coupled motions in this prototypical molecular crystal underlie the observed spectral changes.
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78.70.Dm X-ray absorption spectra
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
61.66.Hq Organic compounds

Study of the sticking of a hydrogen atom on a graphite surface using a mixed classical-quantum dynamics method

S. Morisset, Y. Ferro, and A. Allouche

J. Chem. Phys. 133, 044508 (2010); doi:10.1063/1.3463001 (10 pages)

Online Publication Date: 28 July 2010

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The sticking of one hydrogen atom chemisorbed on the (0001) graphite surface is investigated using a mixed classical-quantum method. The phonon modes of the system in the collinear scattering approach are included in the dynamics calculations. The vibrational degrees of freedom of the surface (phonons) are treated classically, while the H-surface motion is treated using a one-dimensional quantum wave packet propagation method. The sticking probabilities are calculated and the individual contributions of the phonon bands to the collision dynamics are analyzed for surface temperatures of 10, 150, and 300 K and hydrogen kinetic energies ranging from 0.13 to 1.08 eV. An analytical form of the sticking probability as a function of the surface temperature is also proposed.
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
68.35.Ja Surface and interface dynamics and vibrations
68.43.Pq Adsorbate vibrations
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
68.43.Mn Adsorption kinetics

Density functional theory based molecular dynamics study of hydration and electronic properties of aqueous La3+

Cyril Terrier, Pierre Vitorge, Marie-Pierre Gaigeot, Riccardo Spezia, and Rodolphe Vuilleumier

J. Chem. Phys. 133, 044509 (2010); doi:10.1063/1.3460813 (10 pages)

Online Publication Date: 28 July 2010

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Structural and electronic properties of La3+ immersed in bulk water have been assessed by means of density functional theory (DFT)-based Car–Parrinello molecular dynamics (CPMD) simulations. Correct structural properties, i.e., La(III)-water distances and La(III) coordination number, can be obtained within the framework of Car–Parrinello simulations providing that both the La pseudopotential and conditions of the dynamics (fictitious mass and time step) are carefully set up. DFT-MD explicitly treats electronic densities and is shown here to provide a theoretical justification to the necessity of including polarization when studying highly charged cations such as lanthanoids(III) with classical MD. La3+ was found to strongly polarize the water molecules located in the first shell, giving rise to dipole moments about 0.5 D larger than those of bulk water molecules. Finally, analyzing Kohn–Sham orbitals, we found La3+ empty 4f orbitals extremely compact and to a great extent uncoupled from the water conduction band, while the 5d empty orbitals exhibit mixing with unoccupied states of water.
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61.25.Em Molecular liquids
61.20.Ja Computer simulation of liquid structure

The boson peak of silicate glasses: The role of Si–O, Al–O, and Si–N bonds

Nicolas F. Richet, Hitoshi Kawaji, and Tanguy Rouxel

J. Chem. Phys. 133, 044510 (2010); doi:10.1063/1.3462277 (8 pages)

Online Publication Date: 29 July 2010

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The role of Si–O, Al–O, and Si–N bonds on the boson peak of silicate glasses has been investigated from a study of amorphous Si, SiO2, and two calcium aluminosilicates with 0 (Ca28–O) and 4.4 (Ca28–N) mol % Si3N4. The low-frequency part of the vibrational density of states g(ω) has been calculated from inversion of literature data and new heat capacity measurements. As defined by g(ω)/ω2, the boson peak correlates with the excess heat capacity observed with respect to Debye T3 limiting law. That libration of SiO4 tetrahedra represents the main source of low-frequency excitations in silica glass is illustrated by the strong difference between the anomalies of amorphous Si and SiO2 glass and the marked decrease observed for SiO2 phases of increasing density. When Al substitutes for Si, libration of AlO4 tetrahedra appears hampered by the presence of a charge-compensating cation. Rigidification of the silicate network resulting from substitution of N for O causes the boson peak of Ca28–N to be smaller than that of Ca28–O and shifted toward higher frequencies as increased cross-linking hinders libration of SiO4 or AlO4 tetrahedra. In agreement with their universal phenomenology, the calorimetric boson anomalies of Ca28–O and Ca28–N plot on the master curve defined previously by SiO2 and alkali silicate glasses.
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63.50.-x Vibrational states in disordered systems
61.66.-f Structure of specific crystalline solids
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)

Multi-time density correlation functions in glass-forming liquids: Probing dynamical heterogeneity and its lifetime

Kang Kim and Shinji Saito

J. Chem. Phys. 133, 044511 (2010); doi:10.1063/1.3464331 (10 pages)

Online Publication Date: 30 July 2010

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A multi-time extension of a density correlation function is introduced to reveal temporal information about dynamical heterogeneity in glass-forming liquids. We utilize a multi-time correlation function that is analogous to the higher-order response function analyzed in multidimensional nonlinear spectroscopy. Here, we provide comprehensive numerical results of the four-point, three-time density correlation function from longtime trajectories generated by molecular dynamics simulations of glass-forming binary soft-sphere mixtures. We confirm that the two-dimensional representations in both time and frequency domains are sensitive to the dynamical heterogeneity and that these reveal the couplings of correlated motions, which exist over a wide range of time scales. The correlated motions detected by the three-time correlation function are divided into mobile and immobile contributions that are determined from the particle displacement during the first time interval. We show that the peak positions of the correlations are in accord with the information on the non-Gaussian parameters of the van Hove self-correlation function. Furthermore, it is demonstrated that the progressive changes in the second time interval in the three-time correlation function enable us to analyze how correlations in dynamics evolve in time. From this analysis, we evaluated the lifetime of the dynamical heterogeneity and its temperature dependence systematically. Our results show that the lifetime of the dynamical heterogeneity becomes much slower than the α-relaxation time that is determined from the two-point density correlation function when the system is highly supercooled.
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64.70.pm Liquids
64.70.qj Dynamics and criticality
61.20.Ja Computer simulation of liquid structure

Cubic gauche-CN: A superhard metallic compound predicted via first-principles calculations

Xiaoli Wang, Kuo Bao, Fubo Tian, Xing Meng, Changbo Chen, Bowu Dong, Da Li, Bingbing Liu, and Tian Cui

J. Chem. Phys. 133, 044512 (2010); doi:10.1063/1.3464479 (6 pages)

Online Publication Date: 30 July 2010

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In this paper, we suggest a novel potential superhard material, a new carbon nitride phase consisted of sp3 hybridized bonds, possessing a cubic P213 symmetry (8 atoms/cell, labeled by cg-CN) which is similar to cubic gauche nitrogen (cg-N) by first-principles calculations. It is a metallic compound, while most of other superhard materials are insulators or semiconductors. The Vickers hardness of cg-CN is 82.56 GPa, and if we considered the negative effect of metallic component on hardness, it is 54.7 GPa, which is much harder than any other metallic materials. It is found that a three-dimensional C–N network is mainly responsible for the high hardness. Both elastic constant and phonon-dispersion calculations show that this structure remains mechanically and dynamically stable in the pressure ranges from 0 to 100 GPa. Furthermore, we compared our results with many other proposed structures of carbon nitride with 1:1 stoichiometry and found that only cg-CN is the most favorable stable crystal structure. Formation enthalpies calculations demonstrate that this material can be synthesizable at high pressure (12.7–36.4 GPa).
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
61.66.-f Structure of specific crystalline solids
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.dq Other elastic constants
65.40.G- Other thermodynamical quantities
62.20.Qp Friction, tribology, and hardness

Evolution of the isotropic to nematic phase transition in binary mixtures of octylcyanobiphenyl and n-hexane

K. P. Sigdel and G. S. Iannacchione

J. Chem. Phys. 133, 044513 (2010); doi:10.1063/1.3466917 (7 pages)

Online Publication Date: 30 July 2010

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High-resolution calorimetry has been performed to study the effect of dilution by a nonmesogenic, low-molecular weight solvent (linear n-hexane) on the isotropic-nematic (I-N) phase transition in the liquid crystal (LC) octylcyanobiphenyl (8CB) as a function of n-hexane concentration. Numerous temperature scans were performed without continuous mixing for pure 8CB and all mixture samples of n-hexane mole fraction ranging from xhex = 0.02 to 0.12. The I-N specific heat peak remains first-order for all samples and shifts toward lower temperature nonlinearly while the two-phase I+N coexistence width broadens linearly with increasing xhex. Multiple heating and cooling scans are reproducible and indicate phase separation, if it occurs, must be on very short length scales and is reversible. These results may be a consequence of a competition between random dilution effects and the tendency to phase separate. It is shown that solvent dilution of a LC, if miscible and depending on solvent structure, can lead to a controlled altering of the intermolecular potentials and softening of the LC viscoelastic properties.
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64.70.mj Experimental studies of liquid crystal transitions
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
64.75.Cd Phase equilibria of fluid mixtures, including gases, hydrates, etc.
64.75.Bc Solubility
65.20.Jk Studies of thermodynamic properties of specific liquids
back to top Surfaces, Interfaces, and Materials

Stress-strain relation in the collapse of Langmuir monolayer of a dimer of disk shaped moiety

Bharat Kumar, K. A. Suresh, Satyam K. Gupta, and Sandeep Kumar

J. Chem. Phys. 133, 044701 (2010); doi:10.1063/1.3465575 (5 pages)

Online Publication Date: 22 July 2010

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Langmuir monolayer of a novel molecule containing dimer of disk shaped moiety, viz., terephtalic acid bis-[6-(3,6,7,10,11-pentahexyloxy-triphenylen-2-yloxyl)-hexyl] ester (tp-dimer), was studied at air-water interface. The monolayer of the tp-dimer at air-water interface exhibited the coexistence of condensed and gas phases at large area per molecule which on compression transformed to a uniform condensed phase at lower area per molecule (1.80 nm2) and then collapsed at 1.67 nm2. The monolayer film transferred by Langmuir–Blodgett technique onto a hydrophilic silicon substrate was studied using an atomic force microscope. The topography image showed the film to be of height of about 1.5 nm corresponding to the edge-on configuration of the triphenylene moieties. We have studied the collapse of monolayer at air-water interface as a function of compression rate and temperature. We find that the collapse pressure increased with increase in the compression rate. The surface pressure of the monolayer is considered as stress and compression as strain. The strain rate is related to the collapse pressure by a power law similar to that found in the dendrimers. Our studies on the effect of temperature on the collapse pressure of tp-dimer monolayer showed that the collapse pressure decreased with increase in temperature. We have considered the Arrhenius temperature dependence of the strain rate and calculated the activation energy for the collapse of monolayer. Our analysis of the relative area loss as a function of time in the collapse region suggests that the monolayer collapses by the formation of nuclei of three-dimensional crystallites.
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68.60.Bs Mechanical and acoustical properties
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces
68.37.Ps Atomic force microscopy (AFM)
68.35.bm Polymers, organics
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.F- Deformation and plasticity

Observation of surface structure of 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide using high-resolution Rutherford backscattering spectroscopy

Kaoru Nakajima, Atsushi Ohno, Hiroki Hashimoto, Motofumi Suzuki, and Kenji Kimura

J. Chem. Phys. 133, 044702 (2010); doi:10.1063/1.3465578 (7 pages)

Online Publication Date: 22 July 2010

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The surface structures of 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([CnMIM][TFSI], n = 2,4,6) are studied by high-resolution Rutherford backscattering spectroscopy. The average composition of the surface molecular layer is very close to the stoichiometric composition, showing that neither ion is enriched in the surface layer. A detailed analysis indicates that both cations and anions have preferential molecular orientations at the surface. The alkyl chains of the [CnMIM] cations protrude to the vacuum and the CF3 groups of the [TFSI] anions are also pointing toward the vacuum. While the orientation of the [TFSI] anion becomes weaker with increasing alkyl-chain length, the protrusion of the alkyl chain occurs irrespective of the chain length. It was also found that the N(SO2)2 moiety is located nearly at the same depth as the imidazolium ring, suggesting that one of oxygen atoms in [TFSI] is bonded to the hydrogen of the C2 carbon atom of the imidazolium ring.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
61.66.Bi Elemental solids
61.66.Dk Alloys

Hysteresis reversion in graphene field-effect transistors

Zhi-Min Liao, Bing-Hong Han, Yang-Bo Zhou, and Da-Peng Yu

J. Chem. Phys. 133, 044703 (2010); doi:10.1063/1.3460798 (4 pages)

Online Publication Date: 22 July 2010

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To enhance performances of graphene/SiO2 based field-effect transistors (FETs), understanding of the transfer of carriers through the graphene/SiO2 interface is crucial. In this paper, we have studied the temperature dependent transfer characters of graphene FETs. Hysteresis loop is shown to be dominated by trapping/detrapping carriers through the graphene/SiO2 interface.
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85.30.Tv Field effect devices

A thermodynamically consistent determination of surface tension of small Lennard-Jones clusters from simulation and theory

Jan Julin, Ismo Napari, Joonas Merikanto, and Hanna Vehkamäki

J. Chem. Phys. 133, 044704 (2010); doi:10.1063/1.3456184 (6 pages)

Online Publication Date: 22 July 2010

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We have determined the surface tension of small Lennard-Jones clusters using molecular dynamics and Monte Carlo simulation methods as well as density functional theory calculations. For the two simulation methods the surface tension is calculated via a rigorous thermodynamic route using simulation data as input. The capillary approximation of the classical nucleation theory, where the surface tension of a planar surface is used for cluster surface, is found to be quite reasonable even when the cluster size is as small as 100–150 atoms. For smaller cluster sizes the cluster surface tension is considerably lower than the planar value. We have also obtained an approximative value for the Tolman length by extrapolating to the planar limit the difference between the equimolar radius and the radius of the surface of tension. A negative Tolman length is suggested by all the methods used.
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68.03.Cd Surface tension and related phenomena
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations
82.60.Nh Thermodynamics of nucleation
61.20.-p Structure of liquids
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Noninvasive bipolar double-pulsed-field-gradient NMR reveals signatures for pore size and shape in polydisperse, randomly oriented, inhomogeneous porous media

Noam Shemesh, Evren Özarslan, Tal Adiri, Peter J. Basser, and Yoram Cohen

J. Chem. Phys. 133, 044705 (2010); doi:10.1063/1.3454131 (9 pages)

Online Publication Date: 22 July 2010

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Noninvasive characterization of pore size and shape in opaque porous media is a formidable challenge. NMR diffusion-diffraction patterns were found to be exceptionally useful for obtaining such morphological features, but only when pores are monodisperse and coherently placed. When locally anisotropic pores are randomly oriented, conventional diffusion NMR methods fail. Here, we present a simple, direct, and general approach to obtain both compartment size and shape even in such settings and even when pores are characterized by internal field gradients. Using controlled porous media, we show that the bipolar-double-pulsed-field-gradient (bp-d-PFG) methodology yields diffusion-diffraction patterns from which pore size can be directly obtained. Moreover, we show that pore shape, which cannot be obtained by conventional methods, can be directly inferred from the modulation of the signal in angular bp-d-PFG experiments. This new methodology significantly broadens the types of porous media that can be studied using noninvasive diffusion-diffraction NMR.
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76.60.-k Nuclear magnetic resonance and relaxation
66.30.-h Diffusion in solids
61.43.Gt Powders, porous materials

Stability of critical bubble in stretched fluid of square-gradient density-functional model with triple-parabolic free energy

Masao Iwamatsu and Yutaka Okabe

J. Chem. Phys. 133, 044706 (2010); doi:10.1063/1.3458800 (8 pages)

Online Publication Date: 23 July 2010

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The square-gradient density-functional model with triple-parabolic free energy, which was used previously to study the homogeneous bubble nucleation [ M. Iwamatsu, J. Chem. Phys. 129, 104508 (2008) ], is used to study the stability of the critical bubble nucleated within the bulk undersaturated stretched fluid. The stability of the bubble is studied by solving the Schrödinger equation for the fluctuation. The negative eigenvalue corresponds to the unstable growing mode of the fluctuation. Our results show that there is only one negative eigenvalue whose eigenfunction represents the fluctuation that corresponds to the isotropically growing or shrinking nucleus. In particular, this negative eigenvalue survives up to the spinodal point. Therefore, the critical bubble is not fractal or ramified near the spinodal.
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47.55.dd Bubble dynamics
64.60.qe General theory and computer simulations of nucleation

Adsorption and switching properties of a N-benzylideneaniline based molecular switch on a Au(111) surface

László Óvári, Ying Luo, Felix Leyssner, Rainer Haag, Martin Wolf, and Petra Tegeder

J. Chem. Phys. 133, 044707 (2010); doi:10.1063/1.3460647 (8 pages)

Online Publication Date: 23 July 2010

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High resolution electron energy loss spectroscopy has been employed to analyze the adsorption geometry and the photoisomerization ability of the molecular switch carboxy-benzylideneaniline (CBA) adsorbed on Au(111). CBA on Au(111) adopts a planar (trans) configuration in the first monolayer (ML) as well as for higher coverages (up to 6 ML), in contrast to the strongly nonplanar geometry of the molecule in solution. Illumination with UV light of CBA in direct contact with the Au(111) surface ( ≤ 1 ML) caused no changes in the vibrational structure, whereas at higher coverages (>1 ML) pronounced modifications of vibrational features were observed, which we assign to a trans→cis isomerization. Thermal activation induced the back reaction to trans-CBA. We propose that the photoisomerization is driven by a direct (intramolecular) electronic excitation of the adsorbed CBA molecules in the second ML (and above) analogous to CBA in the liquid phase.
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82.30.Qt Isomerization and rearrangement
82.50.Hp Processes caused by visible and UV light

Edge versus interior in the chemical bonding and magnetism of zigzag edged triangular graphene molecules

Michael R. Philpott, Sinisa Vukovic, Yoshiyuki Kawazoe, and William A. Lester, Jr.

J. Chem. Phys. 133, 044708 (2010); doi:10.1063/1.3457673 (8 pages)

Online Publication Date: 26 July 2010

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Ab initio density functional theory calculations show that the CC bond lengths fall into three distinct groups: core, apex, and edge, irrespective of whether the molecular center is a single atom or a C6-ring. The core, with a geometry that approximates infinite graphene, extends to the penultimate triangular row of carbon atoms, except in the vicinity of an apex. Impressed on the core bonds starting at the center is a small increasing length oscillation. The perimeter CC bonds joined at the apex are the shortest in the molecule. The edge carbon atoms are separated from interior atoms by the longest bonds in the molecule. The spin density localized primarily on edge (not apex) carbons with attached hydrogen (A-sublattice) is likely the highest attainable in any graphene molecule. The CC bonds in the high spin section of the edges are uniform in length and longer than perimeter CC bonds in the zigzag edged linear acenes, hexangulenes, annulenes, and benzene. This is attributed to the large number of edge localized nonbonding molecular orbitals (NBMOs) that sequestered π-charge making it unavailable for bonding.
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31.15.A- Ab initio calculations
73.22.Pr Electronic structure of graphene
81.05.ue Graphene
33.15.Dj Interatomic distances and angles
75.50.Xx Molecular magnets
31.15.E- Density-functional theory

Energy barrier of proton transfer at ice surfaces

Eui-Seong Moon, Jinha Yoon, and Heon Kang

J. Chem. Phys. 133, 044709 (2010); doi:10.1063/1.3457379 (7 pages)

Online Publication Date: 27 July 2010

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We estimated the energy barrier of proton transfer on ice film surfaces through the measurement of the H/D exchange kinetics of H2O and D2O molecules. The isotopomeric populations of water molecules and hydronium ions on the surface were monitored by using the techniques of reactive ion scattering and low energy sputtering, respectively, along the progress of the H/D reaction. When hydronium ions were externally added onto an ice film at a temperature of 70 K, a proton was transferred from the hydronium ion mostly to an adjacent water molecule. The proton transfer distance and the H/D exchange rate increased as the temperature increased for 90–110 K. The activation energy of the proton transfer was estimated to be 10±3 kJ mol−1 on a polycrystalline ice film grown at 135 K. The existence of a substantial energy barrier for proton transfer on the ice surface agreed with proton stabilization at the surface. We also examined the H/D exchange reaction on a pure ice film surface at temperatures of 110–130 K. The activation energy of the reaction was estimated to be 17±4 kJ mol−1, which was contributed from the ion pair formation and proton transfer processes on the surface.
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82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
68.55.at Other materials
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)

Kinetic Monte Carlo simulations of anisotropic Si(100) etching: Modeling the chemical origins of characteristic etch morphologies

Ankush Gupta, Brandon S. Aldinger, Marc F. Faggin, and Melissa A. Hines

J. Chem. Phys. 133, 044710 (2010); doi:10.1063/1.3457159 (13 pages)

Online Publication Date: 27 July 2010

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An atomistic, chemically realistic, kinetic Monte Carlo simulator of anisotropic Si(100) etching was developed. Surface silicon atoms were classified on the basis of their local structure, and all atoms of each class were etched with the same rate. A wide variety of morphologies, including rough, striped, and hillocked, was observed. General reactivity trends were correlated with specific morphological features. The production of long rows of unstrained dihydride species, recently observed in NH4F (aq) etching of Si(100), could only be explained by the rapid etching of dihydrides that are adjacent to (strained) monohydrides—so-called “α-dihydrides.” Some etch kinetics promoted the formation of {111}-microfaceted pyramidal hillocks, similar in structure to those observed experimentally during Si(100) etching. Pyramid formation was intrinsic to the etch kinetics. In contrast with previously postulated mechanisms of pyramid formation, no masking agent (e.g., impurity, gas bubble) was required. Pyramid formation was explained in terms of the slow etch rate of the {111} sides, {110} edges, and the dihydride species that terminated the apex of the pyramid. As a result, slow etching of Si(111) surfaces was a necessary, but insufficient, criterion for microfacet formation on Si(100) surfaces.
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61.43.Bn Structural modeling: serial-addition models, computer simulation
81.65.Cf Surface cleaning, etching, patterning
68.35.B- Structure of clean surfaces (and surface reconstruction)
back to top Polymers and Complex Systems
FREE

Second-harmonic generation in conjugated polymer films: A sensitive probe of how bulk polymer crystallinity changes with spin speed

Ian M. Craig, Christopher J. Tassone, Sarah H. Tolbert, and Benjamin J. Schwartz

J. Chem. Phys. 133, 044901 (2010); doi:10.1063/1.3436517 (11 page)

Online Publication Date: 22 July 2010

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In this paper, we examine the second-harmonic generation (SHG) from spin-cast films of the conjugated polymer poly(2-methoxy-5-(2′-ethylhexyloxy)para-phenylenevinylene) (MEH-PPV). We find that the SHG intensity depends strongly on the speed used to spin cast the films. Two-dimensional grazing incidence x-ray diffraction (XRD) experiments show that the bulk crystallinity of the MEH-PPV films varies in the same way with spin speed as the SHG intensity. This strongly suggests that instead of being interface specific, the second-harmonic signal from conjugated polymer films is dominated by the crystalline domains in the bulk. The nonmonotonic dependence of both the SHG intensity and the degree of MEH-PPV crystallinity results from a competition between the shear forces and the solvent evaporation rate during spin coating, which produces a maximum degree of crystallinity for MEH-PPV films spin cast at around 1400 rpm. We also use XRD to show that thermal annealing produces MEH-PPV films with a single degree of bulk crystallinity, independent of how they were originally cast. This allows us to model the angle- and thickness-dependent SHG from annealed MEH-PPV films with a single polarizability tensor. We find that the SHG from MEH-PPV films fits best to a bulk-allowed electric quadrupole mechanism, consistent with the bulk SHG seen in other π-stacked aromatic molecules. Thus, rather than providing information about conjugated polymer interfaces, SHG can be used as a sensitive probe of the local degree of crystallinity in the bulk of conjugated polymer films.
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78.66.Qn Polymers; organic compounds
42.79.Wc Optical coatings
81.40.Gh Other heat and thermomechanical treatments
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Isomerization-induced surface relief gratings formation: A comparison between the probe and the matrix dynamics

M. Saiddine, V. Teboul, and J. M. Nunzi

J. Chem. Phys. 133, 044902 (2010); doi:10.1063/1.3465577 (4 pages)

Online Publication Date: 23 July 2010

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We report molecular dynamics simulations of the effect of the photoisomerization of probe molecules on the nonequilibrium dynamics of a bulk amorphous matrix. Is it the matrix or the probe that drives the dynamics in SRG formation? In the first picture, the probe isomerization induces the motion of the probe inside the matrix. The motion of the probe then induces molecular motions inside the matrix. In the second picture, the probe isomerization induces a modification of the matrix diffusion mechanism. The diffusion of the matrix then induces the motion of the embedded probe. To answer this question, we compare the motion of the probe molecules and the motion of the matrix molecules in various thermodynamic conditions. We show that when the isomerization is switched on, the matrix molecules surrounding the probe move faster than the probe. Around the probe, the structural relaxation time of the matrix molecules is shorter than the probe relaxation time and the diffusion of the matrix molecules is larger than the probe diffusion. These results show that the matrix motions drive the dynamics.
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82.30.Qt Isomerization and rearrangement
64.70.pj Polymers
61.20.Lc Time-dependent properties; relaxation

Properties of knotted ring polymers. I. Equilibrium dimensions

Marc L. Mansfield and Jack F. Douglas

J. Chem. Phys. 133, 044903 (2010); doi:10.1063/1.3457160 (10 pages) | Cited 1 time

Online Publication Date: 27 July 2010

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We report calculations on three classes of knotted ring polymers: (1) simple-cubic lattice self-avoiding rings (SARs), (2) “true” theta-state rings, i.e., SARs generated on the simple-cubic lattice with an attractive nearest-neighbor contact potential (θ-SARs), and (3) ideal, Gaussian rings. Extrapolations to large polymerization index N imply knot localization in all three classes of chains. Extrapolations of our data are also consistent with conjectures found in the literature which state that (1) Rg→ANν asymptotically for ensembles of random knots restricted to any particular knot state, including the unknot; (2) A is universal across knot types for any given class of flexible chains; and (3) ν is equal to the standard self-avoiding walk (SAW) exponent ( ≅ 0.588) for all three classes of chains (SARs, θ-SARs, and ideal rings). However, current computer technology is inadequate to directly sample the asymptotic domain, so that we remain in a crossover scaling regime for all accessible values of N. We also observe that Rg ∼ p−0.27, where p is the “rope length” of the maximally inflated knot. This scaling relation holds in the crossover regime, but we argue that it is unlikely to extend into the asymptotic scaling regime where knots become localized.
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36.20.Hb Configuration (bonds, dimensions)
36.20.Fz Constitution (chains and sequences)
02.60.Ed Interpolation; curve fitting

Properties of knotted ring polymers. II. Transport properties

Marc L. Mansfield and Jack F. Douglas

J. Chem. Phys. 133, 044904 (2010); doi:10.1063/1.3457161 (9 pages)

Online Publication Date: 27 July 2010

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We have calculated the hydrodynamic radius Rh and intrinsic viscosity [η] of both lattice self-avoiding rings and lattice theta-state rings that are confined to specific knot states by our path-integration technique. We observe that naive scaling arguments based on the equilibrium polymer size fail for both the hydrodynamic radius and the intrinsic viscosity, at least over accessible chain lengths. (However, we do conjecture that scaling laws will nevertheless prevail at sufficiently large N.) This failure is attributed to a “double” cross-over. One cross-over effect is the transition from delocalized to localized knotting: in short chains, the knot is distributed throughout the chain, while in long chains it becomes localized in only a portion of the chain. This transition occurs slowly with increasing N. The other cross-over, superimposed upon the first, is the so-called “draining” effect, in which transport properties maintain dependence on local structure out to very large N. The hydrodynamic mobility of knotted rings of the same length and backbone structure is correlated with the average crossing number X of the knots. The same correlation between mobility and knot complexity X has been observed for the gel-electrophoretic mobility of cyclic DNA molecules.
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61.25.he Polymer solutions
66.20.Cy Theory and modeling of viscosity and rheological properties, including computer simulation

Effect of residual attractive interactions in size asymmetric colloidal mixtures: Theoretical analysis and predictions

Ph. Germain

J. Chem. Phys. 133, 044905 (2010); doi:10.1063/1.3456734 (14 pages)

Online Publication Date: 29 July 2010

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We analyze the influence of residual attractions on the static and some dynamic properties of size asymmetric mixtures of “hard-sphere-like” colloids. These attractions, usually neglected in the theoretical analysis, are characterized by a very short range and a moderate strength reflecting the underlying microscopic structure of the colloidal particles. Their effect on the potentials of mean force is analyzed from analytical expressions obtained from low density expansions. The effective potential of the big particle fluid is next considered. An analytical expression is proposed for estimating the deviation with respect to the hard sphere depletion potential. This case is compared to that of mixtures with noninteracting depletants. The important consequences on the binodals and the glass transition lines of the effective fluid are discussed in both cases. This study is next extended to other properties—the specific heat and the low shear viscosity—which incorporate contributions from the two components of the binary mixture.
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82.70.Dd Colloids
64.75.Cd Phase equilibria of fluid mixtures, including gases, hydrates, etc.
61.20.Gy Theory and models of liquid structure
61.25.-f Studies of specific liquid structures

Electrostatic origins of polyelectrolyte adsorption: Theory and Monte Carlo simulations

Lei Wang, Haojun Liang, and Jianzhong Wu

J. Chem. Phys. 133, 044906 (2010); doi:10.1063/1.3463426 (13 pages)

Online Publication Date: 29 July 2010

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Electrostatic interactions may promote or abate polyelectrolyte adsorption onto a charged surface depending on a number of interrelated factors including the surface and polymer charge densities, the salt concentration, and nonelectrostatic interactions such as van der Waals and hydrophobic forces. Even without the nonelectrostatic interactions, the electrostatic behavior of polyelectrolyte systems is often counterintuitive and cannot be explained with conventional theories of polymers or simple electrolytes. In this work, a nonlocal density functional theory (NLDFT) and Monte Carlo simulations are used together to investigate polyelectrolyte adsorption at both oppositely charged and like-charged surfaces (one due to the direct electrostatic attraction and the other due to counterion correlations). The simulation results provide a stringent test of the numerical performance of the NLDFT, in particular for systems containing multivalent counterions where electrostatic correlations are important. A systematic study of the effects of ion valence, salt concentration, and polyion chain length reveals that polyelectrolyte attraction to an oppositely charged surface is nearly a neutralization effect, little influenced by the polyion chain length and counterion valence. Neither the surface mean electrostatic potential nor the integrated local charge density shows no significant sign of charge inversion. Both theory and simulation predict polyelectrolyte adsorption onto a like-charged surface when the system contains multivalent counterions. In that case, the surface excess is sensitive to the surface charge density, the counterion valence, and the salt concentration. The surface mean electrostatic potential shows a clear evidence of charge inversion when two layers of like charges are mediated by multivalent counterions. The theoretical investigations indicate that most likely, the electrostatic correlation mediated by multivalent counterions is responsible for the layer-by-layer assembly of oppositely charged polyelectrolyte films.
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82.45.Wx Polymers and organic materials in electrochemistry
68.43.Mn Adsorption kinetics
73.40.-c Electronic transport in interface structures
82.45.Gj Electrolytes

Linear viscoelasticity of a single semiflexible polymer with internal friction

Tetsuya Hiraiwa and Takao Ohta

J. Chem. Phys. 133, 044907 (2010); doi:10.1063/1.3463427 (7 pages)

Online Publication Date: 30 July 2010

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The linear viscoelastic behaviors of single semiflexible chains with internal friction are studied based on the wormlike-chain model. It is shown that the frequency dependence of the complex compliance in the high frequency limit is the same as that of the Voigt model. This asymptotic behavior appears also for the Rouse model with internal friction. We derive the characteristic times for both the high frequency limit and the low frequency limit and compare the results with those obtained by Khatri et al.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
62.20.D- Elasticity

Reptation of a semiflexible polymer through porous media

Gimoon Nam, Albert Johner, and Nam-Kyung Lee

J. Chem. Phys. 133, 044908 (2010); doi:10.1063/1.3457999 (10 pages)

Online Publication Date: 30 July 2010

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We study the motion of a single stiff semiflexible filament of length S through an array of topological obstacles. By means of scaling arguments and two-dimensional computer simulations, we show that the stiff chain kinetics follows the reptation picture, albeit with kinetic exponents (for the central monomer) different from those for flexible chain reptation. At early times when topological constraints are irrelevant, the chain kinetics is the anisotropic dynamics of a free filament. After the entanglement time τe transverse modes are equilibrated under the topological constraints, but the chain is not yet correlated over its whole length. During the relaxation of longitudinal modes, both the longitudinal fluctuation of the central monomer and the longitudinal correlation length grow as ∼ math. After time τr ∼ S2 chain ends are correlated, the chain then diffuses globally along the tube and tube renewal takes place. In the reptation regime, the longitudinal fluctuation of the central monomer grows like ∼ t1. The opening of the intermediate ∼ math regime, absent for a free filament, is a signature of the reptation process. Although the underlying physics is quite different, the intermediate regime is reminiscent of the internal Rouse mode relaxation found for reptating flexible chains. In most cases asymptotic power laws from scaling could be complemented by prefactors calculated analytically. Our results are supported by two-dimensional Langevin simulations with fixed obstacles via evaluation of the mean squared displacement of the central monomer. The scaling theory can be extended to long semiflexible polymers adopting random-walk equilibrium configurations and should also apply in three dimensions for porous media with pore diameter smaller than the persistence length of the filament.
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36.20.Fz Constitution (chains and sequences)
36.20.Ey Conformation (statistics and dynamics)

Defect mediated turbulence in a locally quasiperiodic chemical medium

Ghislain St-Yves and Jörn Davidsen

J. Chem. Phys. 133, 044909 (2010); doi:10.1063/1.3464493 (7 pages)

Online Publication Date: 30 July 2010

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Under a change of conditions, spiral waves in oscillatory reaction-diffusion media can become unstable and give rise to a multitude of emergent patterns. For example, in bounded domains spiral waves can undergo a resonant Hopf bifurcation leading to period-2 spirals which emit wave trains with doubled wavelength and temporal period and have a characteristic synchronization defect line. Here, we analyze the emergent patterns due to nonresonant Hopf bifurcations in the local dynamics giving rise to quasiperiodicity as reported in systems such as the peroxidase-oxidase and the Belousov–Zhabotinsky reaction. For a conceptual model of the peroxidase-oxidase reaction in a spatially extended medium, we find numerically that the additional frequency leads to defect-mediated turbulence. This proves that defect-mediated turbulence can indeed exist in media where the underlying local dynamics is quasiperiodic. While many statistical features of this turbulent dynamics are similar to those observed for other systems, we show that there are clear differences if higher-order statistics are considered. In particular, we find that the space-time dynamics of the topological defects as characterized by the statistics of defect loops is closely related to the underlying local dynamics.
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82.40.Bj Oscillations, chaos, and bifurcations
82.20.-w Chemical kinetics and dynamics
47.35.-i Hydrodynamic waves
47.70.Fw Chemically reactive flows
82.40.Ck Pattern formation in reactions with diffusion, flow and heat transfer
47.54.Bd Theoretical aspects
back to top Biological Molecules, Biopolymers, and Biological Systems

Polymer translocation through α-hemolysin pore with tunable polymer-pore electrostatic interaction

Chiu Tai Andrew Wong and M. Muthukumar

J. Chem. Phys. 133, 045101 (2010); doi:10.1063/1.3464333 (12 pages)

Online Publication Date: 23 July 2010

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We have measured the ionic current blockages produced by single molecules of sodium poly(styrene sulfonate) passing through an α-hemolysin protein pore under an electric field. Most of the blockage events were composed of one or two blockage levels of ionic current. By analyzing the statistics of different event types for different polymer lengths, applied voltages, and pH conditions, we have identified the molecular mechanism behind the two-level blockages. Our analysis of the data shows that not all blockages are successful translocation events and the propensity of successful translocation can be tuned by pH gradients across the protein pore. We interpret our results as the change in protein-polymer interaction via protonation of charged amino acid residues of α-hemolysin pore. In addition, we have constructed a stochastic theory for polymer translocation through α-hemolysin pore with tunable polymer-pore interactions. The theoretical calculations capture many features observed in our experiments.
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87.15.R- Reactions and kinetics
87.15.Pc Electronic and electrical properties
87.15.Vv Diffusion

Finite-width bundle is most stable in a solution with salt

Takuya Saito and Kenichi Yoshikawa

J. Chem. Phys. 133, 045102 (2010); doi:10.1063/1.3458690 (6 pages)

Online Publication Date: 23 July 2010

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We applied the mean-field approach to a columnar bundle assembled by the parallel arrangement of stiff polyelectrolyte rods in a salt bath. The electrostatic potential can be divided into two regions: inside the bundle for condensed counterions and outside the bundle for free small ions. To determine the distribution of condensed counterions inside the bundle, we use a local self-consistent condition that depends on the charge density, the electrostatic potential, and the net polarization. The results showed that, upon bundle formation, the electric charge of polyelectrolytes, even those inside the bundle, tends to survive in an inhomogeneous manner, and thus their width remains finite under thermal equilibrium because of the long-range effect of charge instability.
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82.35.Rs Polyelectrolytes
82.45.Gj Electrolytes
66.30.hk Polymers
31.15.xr Self-consistent-field methods
34.70.+e Charge transfer
82.45.Wx Polymers and organic materials in electrochemistry

Entropic potential field formed for a linear-motor protein near a filament: Statistical-mechanical analyses using simple models

Ken-ichi Amano, Takashi Yoshidome, Mitsuhiro Iwaki, Makoto Suzuki, and Masahiro Kinoshita

J. Chem. Phys. 133, 045103 (2010); doi:10.1063/1.3462279 (11 page)

Online Publication Date: 27 July 2010

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We report a new progress in elucidating the mechanism of the unidirectional movement of a linear-motor protein (e.g., myosin) along a filament (e.g., F-actin). The basic concept emphasized here is that a potential field is entropically formed for the protein on the filament immersed in solvent due to the effect of the translational displacement of solvent molecules. The entropic potential field is strongly dependent on geometric features of the protein and the filament, their overall shapes as well as details of the polyatomic structures. The features and the corresponding field are judiciously adjusted by the binding of adenosine triphosphate (ATP) to the protein, hydrolysis of ATP into adenosine diphosphate (ADP)+Pi, and release of Pi and ADP. As the first step, we propose the following physical picture: The potential field formed along the filament for the protein without the binding of ATP or ADP+Pi to it is largely different from that for the protein with the binding, and the directed movement is realized by repeated switches from one of the fields to the other. To illustrate the picture, we analyze the spatial distribution of the entropic potential between a large solute and a large body using the three-dimensional integral equation theory. The solute is modeled as a large hard sphere. Two model filaments are considered as the body: model 1 is a set of one-dimensionally connected large hard spheres and model 2 is a double helical structure formed by two sets of connected large hard spheres. The solute and the filament are immersed in small hard spheres forming the solvent. The major findings are as follows. The solute is strongly confined within a narrow space in contact with the filament. Within the space there are locations with sharply deep local potential minima along the filament, and the distance between two adjacent locations is equal to the diameter of the large spheres constituting the filament. The potential minima form a ringlike domain in model 1 while they form a pointlike one in model 2. We then examine the effects of geometric features of the solute on the amplitudes and asymmetry of the entropic potential field acting on the solute along the filament. A large aspherical solute with a cleft near the solute-filament interface, which mimics the myosin motor domain, is considered in the examination. Thus, the two fields in our physical picture described above are qualitatively reproduced. The factors to be taken into account in further studies are also discussed.
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87.16.Nn Motor proteins (myosin, kinesin dynein)
87.14.E- Proteins

Dominant reaction pathways in protein folding: A direct validation against molecular dynamics simulations

Pietro Faccioli, Alice Lonardi, and Henri Orland

J. Chem. Phys. 133, 045104 (2010); doi:10.1063/1.3459097 (6 pages)

Online Publication Date: 29 July 2010

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The dominant reaction pathway (DRP) is an algorithm to microscopically compute the most probable reaction pathways in the overdamped Langevin dynamics without investing computational time in simulating the local thermal motion in the metastable configurations. In order to test the accuracy of such a method, we investigate the dynamics of the folding of a β hairpin within a model that accounts for both native and non-native interactions. We compare the most probable folding pathways calculated with the DRP method with the folding trajectories obtained directly from molecular dynamics simulations. We find that the two approaches give consistent results.
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87.15.ap Molecular dynamics simulation
31.50.Df Potential energy surfaces for excited electronic states
87.14.E- Proteins
87.15.Cc Folding: thermodynamics, statistical mechanics, models, and pathways
87.15.R- Reactions and kinetics
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Comment on “Evaluation of surface tension and Tolman length as a function of droplet radius from experimental nucleation rate and supersaturation ratio: Metal vapor homogeneous nucleation” [ J. Chem. Phys. 124, 014506 (2006) ]

J. Liu and S. C. Garrick

J. Chem. Phys. 133, 047101 (2010); doi:10.1063/1.3420649 (2 pages)

Online Publication Date: 27 July 2010

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Abstract Unavailable
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68.03.Cd Surface tension and related phenomena
64.60.qe General theory and computer simulations of nucleation
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Response to “Comment on ‘Evaluation of surface tension and Tolman length as a function of droplet radius from experimental nucleation rate and supersaturation ratio: Metal vapor homogeneous nucleation’ ” [J. Chem. Phys. 133, 047101 (2010)]

S. V. Vosel, A. A. Onischuk, and P. A. Purtov

J. Chem. Phys. 133, 047102 (2010); doi:10.1063/1.3469784 (3 pages)

Online Publication Date: 27 July 2010

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Abstract Unavailable
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68.03.Cd Surface tension and related phenomena
64.60.qe General theory and computer simulations of nucleation
64.70.Hz Solid-vapor transitions
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Comment on “Ab initio molecular dynamics calculation of ion hydration free energies” [ J. Chem. Phys. 130, 204507 (2009) ]

Edward S. Chen and Edward C. M. Chen

J. Chem. Phys. 133, 047103 (2010); doi:10.1063/1.3456164 (2 pages) | Cited 1 time

Online Publication Date: 27 July 2010

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We suggest that the authors compare their theoretical Gibbs free energies −ΔGhyd (kcal/mol) Li+, 128(1), 135; Cl−, 78(1), 70(2); and Ag+, 120(1) to recent absolute experimental values Li+, 128; Cl−, 74; and Ag+, 119 kcal/mol referenced to that for H+, 266(2) kcal/mol. We present bulk Gibbs hydration free energies and ionic radii for other ions from aqueous electron affinities, monohydration free energies, and diatomic halogen anion potential energy curves consistent with the Born dielectric constant, 3.4, for electrons and protons.
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31.15.A- Ab initio calculations
31.15.xv Molecular dynamics and other numerical methods
32.50.+d Fluorescence, phosphorescence (including quenching)
31.50.-x Potential energy surfaces
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Response to “Comment on ‘Ab initio molecular dynamics calculation of ion hydration free energies’  [J. Chem. Phys. 133, 047103 (2010)]”

Susan B. Rempe and Kevin Leung

J. Chem. Phys. 133, 047104 (2010); doi:10.1063/1.3456167 (2 pages)

Online Publication Date: 27 July 2010

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Abstract Unavailable
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31.15.A- Ab initio calculations
05.70.Ce Thermodynamic functions and equations of state
31.15.xv Molecular dynamics and other numerical methods
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Publisher’s Note: “Molecular anion formation in 9,10-anthraquinone: Dependence of the electron detachment rate on temperature and incident electron energy” [J. Chem. Phys. 132, 244313 (2010)]

Stanislav A. Pshenichnyuk, Alexander S. Vorob’ev, Nail L. Asfandiarov, and Alberto Modelli

J. Chem. Phys. 133, 049901 (2010); doi:10.1063/1.3471378 (1 page)

Online Publication Date: 23 July 2010

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Abstract Unavailable
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34.80.Gs Molecular excitation and ionization
34.50.Gb Electronic excitation and ionization of molecules
34.80.Ht Dissociation and dissociative attachment
99.10.Fg Publisher's note
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Erratum: “Bimolecular reaction rates from ring polymer molecular dynamics” [ J. Chem. Phys. 130, 174713 (2009) ]

Rosana Collepardo-Guevara, Yury V. Suleimanov, and David E. Manolopoulos

J. Chem. Phys. 133, 049902 (2010); doi:10.1063/1.3464477 (2 pages)

Online Publication Date: 30 July 2010

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Abstract Unavailable
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99.10.Cd Errata
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