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14 Oct 2008

Volume 129, Issue 14, Articles (14xxxx)

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back to top Theoretical Methods and Algorithms

Approximate treatment of higher excitations in coupled-cluster theory. II. Extension to general single-determinant reference functions and improved approaches for the canonical Hartree–Fock case

Mihály Kállay and Jürgen Gauss

J. Chem. Phys. 129, 144101 (2008); http://dx.doi.org/10.1063/1.2988052 (9 pages) | Cited 10 times

Online Publication Date: 8 October 2008

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The theory and implementation of approximate coupled-cluster (CC), in particular approximate CC singles, doubles, triples, and quadruples methods, are discussed for general single-determinant reference functions. While the extension of iterative approximate models to the non-Hartree–Fock case is straightforward, the generalization of perturbative approaches is not trivial. In contrast to the corresponding perturbative triples methods, there are additional terms required for non-Hartree–Fock reference functions, and there are several possibilities to derive approximations to these terms. As it turns out impossible to develop an approach that is consistent with the canonical Hartree–Fock-based theory, several new approximations have been implemented and their performance for total energies and heats of formation has been assessed. The numerical results show that the performance of the methods does not depend strongly on the approximations assumed. Furthermore, the new perturbative quadruples methods, when applied to canonical Hartree–Fock reference functions, outperform at least for absolute energies the existing ones without increasing the computational costs.
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31.15.bw Coupled-cluster theory
31.15.xr Self-consistent-field methods
31.15.xp Perturbation theory
82.60.Cx Enthalpies of combustion, reaction, and formation
82.20.Kh Potential energy surfaces for chemical reactions

A molecular dynamics study of the phase transition in bcc metal nanoparticles

Yasushi Shibuta and Toshio Suzuki

J. Chem. Phys. 129, 144102 (2008); http://dx.doi.org/10.1063/1.2991435 (10 pages) | Cited 24 times

Online Publication Date: 8 October 2008

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The phase transition between liquid and solid phases in body-centered cubic (bcc) metal nanoparticles of iron, chromium, molybdenum, and tungsten with size ranging from 2000 to 31250 atoms was investigated using a molecular dynamics simulation. The nucleation from an undercooled liquid droplet was observed during cooling in all nanoparticles considered. It was found that a nucleus was generated near one side of the particle and solidification spread toward the other side the during nucleation process. On the other hand, the surface melting and subsequent inward melting of the solid core of the nanoparticles were observed during heating. The depression of the melting point was proportional to the inverse of the particle radius due to the Gibbs–Thomson effect. On the other hand, the depression of the nucleation temperature during cooling was not monotonic with respect to the particle radius since the nucleation from an undercooled liquid depends on the event probability of an embryo or a nucleus.
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64.70.dj Melting of specific substances
64.60.qj Studies of nucleation in specific substances
81.30.Fb Solidification
68.35.Rh Phase transitions and critical phenomena
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems

Correlation between conductivity or diffusivity and activation energy in amorphous solids

Manju Sharma and S. Yashonath

J. Chem. Phys. 129, 144103 (2008); http://dx.doi.org/10.1063/1.2990744 (10 pages) | Cited 3 times

Online Publication Date: 8 October 2008

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There exist many investigations of ionic transport in a variety of glasses. These studies exhibit strong correlation between ionic conductivity and activation energy: Typically, it is found that higher conductivity is associated with lower activation energies and vice versa. Although there are explanations for this at a phenomenological level, there is no consistent physical picture to explain the correlation between conductivity and activation energy. We have carried out molecular dynamics simulation as a function of the size of the impurity atom or diffusant (both neutral and charged) in a host amorphous matrix. We find that there is a maximum in self-diffusivity as a function of the size of the impurity atom suggesting that there is an appropriate size for which the diffusivity is maximum. The activation energy is found to be the lowest for this size of the impurity. A similar maximum has been previously found in other condensed phases, such as confined fluids and dense liquids, and has its origin in the levitation effect. The implications of this result for understanding ionic conductivity in glasses are discussed. Our results suggest that there is a relation between microscopic structure of the amorphous solid, diffusivity or conductivity, and activation energy. The nature of this relationship is discussed in terms of the levitation parameter showing that diffusivity is maximum when the size of the neck or doorway radius is comparable with the size of the diffusant. Our computational results here are in excellent agreement with independent experimental results of Nascimento et al. [ Braz. J. Phys. 35, 626 (2005) ] that structural features of the glass are important in determining the ionic conductivity.
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66.30.hh Glasses
66.30.J- Diffusion of impurities
61.43.Bn Structural modeling: serial-addition models, computer simulation

Correlation functions in quantized Hamilton dynamics and quantal cumulant dynamics

Yuriy V. Pereverzev, Andrey Pereverzev, Yasuteru Shigeta, and Oleg V. Prezhdo

J. Chem. Phys. 129, 144104 (2008); http://dx.doi.org/10.1063/1.2990005 (7 pages) | Cited 2 times

Online Publication Date: 9 October 2008

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Quantized Hamilton dynamics (QHD) [ O. V. Prezhdo and Y. V. Pereverzev, J. Chem. Phys. 113, 6557 (2000) ] and quantal cumulant dynamics (QCD) [ Shigeta et al., J. Chem. Phys. 125, 244102 (2006) ] are used to obtain a semiclassical description of two-time correlation functions (CFs). Generally, lower-order CFs couple to higher-order CFs. The infinite hierarchy is terminated by a closure, which neglects higher-order irreducible correlators and provides an efficient approximation to quantum mechanics. The approach is illustrated with a simple nonlinear system, for which the real part of the classical CF continues a perfect oscillation and the imaginary part is identically zero. At little computational expense, the second-order QHD/QCD approximation reproduces the real and imaginary parts of the quantum-mechanical CF.
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31.15.V- Electron correlation calculations for atoms, ions and molecules
31.15.bt Statistical model calculations (including Thomas-Fermi and Thomas-Fermi-Dirac models)

Interpreting the Coulomb-field approximation for generalized-Born electrostatics using boundary-integral equation theory

Jaydeep P. Bardhan

J. Chem. Phys. 129, 144105 (2008); http://dx.doi.org/10.1063/1.2987409 (12 pages) | Cited 7 times

Online Publication Date: 9 October 2008

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The importance of molecular electrostatic interactions in aqueous solution has motivated extensive research into physical models and numerical methods for their estimation. The computational costs associated with simulations that include many explicit water molecules have driven the development of implicit-solvent models, with generalized-Born (GB) models among the most popular of these. In this paper, we analyze a boundary-integral equation interpretation for the Coulomb-field approximation (CFA), which plays a central role in most GB models. This interpretation offers new insights into the nature of the CFA, which traditionally has been assessed using only a single point charge in the solute. The boundary-integral interpretation of the CFA allows the use of multiple point charges, or even continuous charge distributions, leading naturally to methods that eliminate the interpolation inaccuracies associated with the Still equation. This approach, which we call boundary-integral-based electrostatic estimation by the CFA (BIBEE/CFA), is most accurate when the molecular charge distribution generates a smooth normal displacement field at the solute-solvent boundary, and CFA-based GB methods perform similarly. Conversely, both methods are least accurate for charge distributions that give rise to rapidly varying or highly localized normal displacement fields. Supporting this analysis are comparisons of the reaction-potential matrices calculated using GB methods and boundary-element-method (BEM) simulations. An approximation similar to BIBEE/CFA exhibits complementary behavior, with superior accuracy for charge distributions that generate rapidly varying normal fields and poorer accuracy for distributions that produce smooth fields. This approximation, BIBEE by preconditioning (BIBEE/P), essentially generates initial guesses for preconditioned Krylov-subspace iterative BEMs. Thus, iterative refinement of the BIBEE/P results recovers the BEM solution; excellent agreement is obtained in only a few iterations. The boundary-integral-equation framework may also provide a means to derive rigorous results explaining how the empirical correction terms in many modern GB models significantly improve accuracy despite their simple analytical forms.
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31.15.xv Molecular dynamics and other numerical methods
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions
02.60.Lj Ordinary and partial differential equations; boundary value problems

Adsorption of inert gases including element 118 on noble metal and inert surfaces from ab initio Dirac–Coulomb atomic calculations

V. Pershina, A. Borschevsky, E. Eliav, and U. Kaldor

J. Chem. Phys. 129, 144106 (2008); http://dx.doi.org/10.1063/1.2988318 (9 pages) | Cited 7 times

Online Publication Date: 9 October 2008

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The interaction of the inert gases Rn and element 118 with various surfaces has been studied on the basis of fully relativistic ab initio Dirac–Coulomb CCSD(T) calculations of atomic properties. The calculated polarizability of element 118, 46.3 a.u., is the largest in group 18, the ionization potential is the lowest at 8.91 eV, and the estimated atomic radius is the largest, 4.55 a.u. These extreme values reflect, in addition to the general trends in the Periodic Table, the relativistic expansion and destabilization of the outer valence 7p3/2 orbital. Van der Waals coefficients C3 and adsorption enthalpies ΔHads of Ne through element 118 on noble metals and inert surfaces, such as quartz, ice, Teflon, and graphite, were calculated in a physisorption model using the atomic properties obtained. The C3 coefficients were shown to steadily increase in group 18, while the increase in ΔHads from Ne to Rn does not continue to element 118: The large atomic radius of the latter element is responsible for a decrease in the interaction energy. We therefore predict that experimental distinction between Rn and 118 by adsorption on these types of surfaces will not be feasible. A possible candidate for separating the two elements is charcoal; further study is needed to test this possibility.
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68.43.Bc Ab initio calculations of adsorbate structure and reactions
51.30.+i Thermodynamic properties, equations of state

Multibody scattering, correlation, molecular conduction, and the 0.7 anomaly

Joseph E. Subotnik and Abraham Nitzan

J. Chem. Phys. 129, 144107 (2008); http://dx.doi.org/10.1063/1.2988495 (14 pages) | Cited 2 times

Online Publication Date: 10 October 2008

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We describe a new grid-based (or localized orbital-based) method for treating the effects of exchange and correlation on electronic transmission through a molecular target where there are initially other bound electrons. Our algorithm combines the approaches of (i) solid-state grid-based algorithms using self-energies and (ii) the complex Kohn method from electron-molecule scattering. For the general problem of a molecular target with n-electrons, our algorithm should ideally solve for electronic transmission with a computational cost scaling as n2, although the present implementation is limited to one-dimensional problems. In this paper, we implement our algorithm to solve three one-dimensional model problems involving two electrons: (i) Single-channel resonant transmission through a double-barrier well (DBW), where the target already contains one bound-state electron [ Rejec et al., Phys. Rev. B 67, 075311 (2003) ]; (ii) multichannel resonant transmission through a DBW, where the incoming electron can exchange energy with the bound electron; (iii) transmission through a triple-barrier well (TBW), where the incoming electron can knock forward the bound electron, yielding a physical model of electron-assisted electron transfer. This article offers some insight about the role and size of exchange and correlation effects in molecular conduction, where few such rigorous calculations have yet been made. Such multibody effects have already been experimentally identified in mesoscopic electron transport, giving rise to the “0.7 anomaly,” whereby electrons traveling through a narrow channel pair up as singlets and triplets. We expect the effect of electronic correlation to be even more visible for conduction through molecules, where electrons should partially localize into bonding and antibonding orbitals.
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71.70.Gm Exchange interactions
73.23.-b Electronic transport in mesoscopic systems
73.30.+y Surface double layers, Schottky barriers, and work functions

The relative entropy is fundamental to multiscale and inverse thermodynamic problems

M. Scott Shell

J. Chem. Phys. 129, 144108 (2008); http://dx.doi.org/10.1063/1.2992060 (7 pages) | Cited 20 times

Online Publication Date: 10 October 2008

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We show that the relative entropy, Srel ≡ ∑pT ln(pT/pM), provides a fundamental and unifying framework for multiscale analysis and for inverse molecular-thermodynamic problems involving optimization of a model system (M) to reproduce the properties of a target one (T). We demonstrate that the relative entropy serves as a generating function for principles in variational mean-field theory and uniqueness and gives intuitive results for simple case scenarios in model development. Moreover, we suggest that the relative entropy provides a rigorous framework for multiscale simulations and offers new numerical techniques for linking models at different scales. Finally, we show that Srel carries physical significance by using it to quantify the deviations of a three-site model of water from simple liquids, finding that the relative entropy, a thermodynamic concept, even predicts water’s kinetic anomalies.
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65.20.Jk Studies of thermodynamic properties of specific liquids
61.20.Gy Theory and models of liquid structure

Real space method for the electronic structure of one-dimensional periodic systems

Jiaxin Han, Murilo L. Tiago, T.-L. Chan, and James R. Chelikowsky

J. Chem. Phys. 129, 144109 (2008); http://dx.doi.org/10.1063/1.2988316 (7 pages) | Cited 3 times

Online Publication Date: 10 October 2008

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We present a real space pseudopotential method for calculating the electronic structure of one-dimensional periodic systems such as nanowires. As an application of this method, we examine H-passivated Si nanowires. The band structure and heat of formation of the Si nanowires are presented and compared to plane wave methods. Our method is able to offer the same accuracy as the traditional plane wave methods but offers a number of computational advantages such as faster convergence for heteropolar nanowires.
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71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)
71.20.Mq Elemental semiconductors
73.21.Hb Quantum wires

The role of dimensionality on the quenching of spin-orbit effects in the optics of gold nanostructures

Alberto Castro, Miguel A. L. Marques, Aldo H. Romero, Micael J. T. Oliveira, and Angel Rubio

J. Chem. Phys. 129, 144110 (2008); http://dx.doi.org/10.1063/1.2990745 (4 pages) | Cited 8 times

Online Publication Date: 13 October 2008

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By first-principles time-dependent density-functional calculations, we show the relevance of relativistic effects to shape the photoabsorption cross section of small gold clusters (Aun, n ⩽ 8, and n = 20) and small nanowires (n ⩽ 7). The relativistic effects not only dictate the stabilization of planar geometries (as it has already been shown by treating the core electrons relativistically): The spin-orbit coupling also has a strong impact in the absorption spectra (resonances and oscillator strengths). This is especially true for nanowires, where the effect of spin orbit is large and not substantially reduced with the chain length, in contrast to more compact gold clusters where this spin-orbit effect tends to be quenched. These results have far reaching consequences in fields such as electronic transport, where gold nanowires are often used, but where spin-orbit effects are generally disregarded.
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36.40.Vz Optical properties of clusters
36.40.Cg Electronic and magnetic properties of clusters
36.40.Mr Spectroscopy and geometrical structure of clusters
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
31.15.aj Relativistic corrections, spin-orbit effects, fine structure; hyperfine structure
31.15.ee Time-dependent density functional theory

Two complementary molecular energy decomposition schemes: The Mayer and Ziegler–Rauk methods in comparison

Sergei F. Vyboishchikov, Andreas Krapp, and Gernot Frenking

J. Chem. Phys. 129, 144111 (2008); http://dx.doi.org/10.1063/1.2989805 (12 pages) | Cited 2 times

Online Publication Date: 14 October 2008

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In the present paper we discuss and compare two different energy decomposition schemes: Mayer’s Hartree–Fock energy decomposition into diatomic and monoatomic contributions [ Chem. Phys. Lett. 382, 265 (2003) ], and the Ziegler–Rauk dissociation energy decomposition [ Inorg. Chem. 18, 1558 (1979) ]. The Ziegler–Rauk scheme is based on a separation of a molecule into fragments, while Mayer’s scheme can be used in the cases where a fragmentation of the system in clearly separable parts is not possible. In the Mayer scheme, the density of a free atom is deformed to give the one-atom Mulliken density that subsequently interacts to give rise to the diatomic interaction energy. We give a detailed analysis of the diatomic energy contributions in the Mayer scheme and a close look onto the one-atom Mulliken densities. The Mulliken density ρA has a single large maximum around the nuclear position of the atom A, but exhibits slightly negative values in the vicinity of neighboring atoms. The main connecting point between both analysis schemes is the electrostatic energy. Both decomposition schemes utilize the same electrostatic energy expression, but differ in how fragment densities are defined. In the Mayer scheme, the electrostatic component originates from the interaction of the Mulliken densities, while in the Ziegler–Rauk scheme, the undisturbed fragment densities interact. The values of the electrostatic energy resulting from the two schemes differ significantly but typically have the same order of magnitude. Both methods are useful and complementary since Mayer’s decomposition focuses on the energy of the finally formed molecule, whereas the Ziegler–Rauk scheme describes the bond formation starting from undeformed fragment densities.
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31.15.xr Self-consistent-field methods
33.15.Fm Bond strengths, dissociation energies
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy

Solvent effects on optical properties of molecules: A combined time-dependent density functional theory/effective fragment potential approach

Soohaeng Yoo, Federico Zahariev, Sarom Sok, and Mark S. Gordon

J. Chem. Phys. 129, 144112 (2008); http://dx.doi.org/10.1063/1.2992049 (8 pages) | Cited 18 times

Online Publication Date: 14 October 2008

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A quantum mechanics/molecular mechanics (QM/MM) type of scheme is employed to calculate the solvent-induced shifts of molecular electronic excitations. The effective fragment potential (EFP) method was used for the classical potential. Since EFP has a density dependent functional form, in contrast with most other MM potentials, time-dependent density functional theory (TDDFT) has been modified to combine TDDFT with EFP. This new method is then used to perform a hybrid QM/MM molecular dynamics simulation to generate a simulated spectrum of the n→π∗ vertical excitation energy of acetone in vacuum and with 100 water molecules. The calculated water solvent effect on the vertical excitation energy exhibits a blueshift of the n→π∗ vertical excitation energy in acetone (Δω1 = 0.211 eV), which is in good agreement with the experimental blueshift.
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33.70.Jg Line and band widths, shapes, and shifts
31.15.es Applications of density-functional theory (e.g., to electronic structure and stability; defect formation; dielectric properties, susceptibilities; viscoelastic coefficients; Rydberg transition frequencies)
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)

Nonequilibrium fluctuation-dissipation theorem of Brownian dynamics

L. Y. Chen

J. Chem. Phys. 129, 144113 (2008); http://dx.doi.org/10.1063/1.2992153 (4 pages) | Cited 9 times

Online Publication Date: 14 October 2008

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Studying the Brownian motion of a system driven by an external control from one macroscopic state to another macroscopic state, this paper presents the derivation of a nonlinear fluctuation-dissipation theorem (FDT). The new FDT relates the nonequilibrium work to the equilibrium free-energy difference in a very simple manner. It is valid wherever the Brownian dynamics is applicable. It recovers the well-known Crooks fluctuation theorem (CFT) within the quasiequilibrium regime where the dissipative work is nearly zero. It will also be shown that the CFT’s fundamental assumption of microscopic reversibility is not obeyed in experiments such as mechanically unfolding biological molecules, in which the external driving forces depend on the system’s coordinates.
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05.40.Jc Brownian motion
05.70.Ln Nonequilibrium and irreversible thermodynamics
87.15.hm Folding dynamics
82.20.Wt Computational modeling; simulation
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

Rotational spectrum and molecular properties of pyridine⋯xenon

Shouyuan Tang, Luca Evangelisti, Biagio Velino, and Walther Caminati

J. Chem. Phys. 129, 144301 (2008); http://dx.doi.org/10.1063/1.2990747 (6 pages) | Cited 4 times

Online Publication Date: 8 October 2008

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The rotational spectra of six isotopologues of pyridine-xenon, two isotopes of the nitrogen atom (14N and 15N) in pyridine with three isotopes of the rare gas atom (129Xe, 131Xe, and 132Xe) have been measured by pulsed jet Fourier transform microwave spectroscopy. The complex has a structure with the xenon atom located in the plane of symmetry perpendicular to the aromatic ring plane. Its distance from the center of mass of pyridine is 3.81 Å, and it is tilted—with respect to the c principal axis of pyridine—by 7° toward the N atom. The 14N and 131Xe nuclear quadrupole coupling constants have been determined for the isotopologues containing these nuclei. Information on the dynamics of the Xe van der Waals motions was obtained from the centrifugal distortion and from the changes in the planar moments of inertia in going from pyridine to pyridine⋯Xe.
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33.20.Sn Rotational analysis
33.25.+k Nuclear resonance and relaxation
33.15.Bh General molecular conformation and symmetry; stereochemistry
34.20.Gj Intermolecular and atom-molecule potentials and forces
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Bx Radio-frequency and microwave spectra

Laser detection of spin-polarized hydrogen from HCl and HBr photodissociation: Comparison of H- and halogen-atom polarizations

Dimitris Sofikitis, Luis Rubio-Lago, Lykourgos Bougas, Andrew J. Alexander, and T. Peter Rakitzis

J. Chem. Phys. 129, 144302 (2008); http://dx.doi.org/10.1063/1.2989803 (10 pages) | Cited 5 times

Online Publication Date: 8 October 2008

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Thermal HCl and HBr molecules were photodissociated using circularly polarized 193 nm light, and the speed-dependent spin polarization of the H-atom photofragments was measured using polarized fluorescence at 121.6 nm. Both polarization components, described by the a01(⊥) and Re[a11(∥,⊥)] parameters which arise from incoherent and coherent dissociation mechanisms, are measured. The values of the a01(⊥) parameter, for both HCl and HBr photodissociation, are within experimental error of the predictions of both ab initio calculations and of previous measurements of the polarization of the halide cofragments. The experimental and ab initio theoretical values of the Re[a11(∥,⊥)] parameter show some disagreement, suggesting that further theoretical investigations are required. Overall, good agreement occurs despite the fact that the current experiments photodissociate molecules at 295 K, whereas previous measurements were conducted at rotational temperatures of about 15 K.
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33.80.Gj Diffuse spectra; predissociation, photodissociation
33.50.Dq Fluorescence and phosphorescence spectra
31.15.A- Ab initio calculations

Vibrational energy transfer between I2(B 3Π0u+,ν′ = 21) and He at very low temperatures: Impulsive versus complex formation mechanisms assisted by tunneling through the centrifugal barrier

Iván Cabanillas-Vidosa, Carlos A. Rinaldi, Gustavo A. Pino, and Juan C. Ferrero

J. Chem. Phys. 129, 144303 (2008); http://dx.doi.org/10.1063/1.2987706 (9 pages) | Cited 5 times

Online Publication Date: 8 October 2008

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The temperature dependence of the state-to-state vibrational relaxation rate constant (kν21−Δν) for collisions between I2(B,ν′ = 21) and He at very low kinetic energies was studied. The fluorescence from I2(B,ν′ = 21−Δν′) with Δν′ = 1–5 indicates that in the temperature range of 0.6–8.2 K these states are populated by only one collision with He. The behavior of kν21−Δν with temperature can be divided into two groups. The group with quantum changes Δν′ = 1–3 shows scattering resonances in the low temperature region, with a general monotonical decrease of the rate constant with temperature, suggesting the importance of van der Waals interactions. This behavior is supported by the calculation of the probability of tunneling through the centrifugal barriers. For collisions in which 4–5 quanta are lost in a single event, there are no evidences of scattering resonances and the values of the relaxation rate constants could be determined only at the highest temperatures of this study. This suggests that relaxation occurs via impulsive collisions. The branching ratios for each channel are also temperature dependent and this behavior also suggests that the energy transfer mechanism changes with Δν′.
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34.50.Ez Rotational and vibrational energy transfer
33.50.Dq Fluorescence and phosphorescence spectra

Theoretical investigation of intramolecular vibrational energy redistribution in HFCO and DFCO induced by an external field

Gauthier Pasin, Christophe Iung, Fabien Gatti, Falk Richter, Céline Léonard, and Hans-Dieter Meyer

J. Chem. Phys. 129, 144304 (2008); http://dx.doi.org/10.1063/1.2991411 (10 pages) | Cited 2 times

Online Publication Date: 8 October 2008

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The present paper is devoted to a full quantum mechanical study of the intramolecular vibrational energy redistribution in HFCO and DFCO. In contrast to our previous studies [ Pasin et al., J. Chem. Phys. 124, 194304 (2006) and 126, 024302 (2007) ], the dynamics is now performed in the presence of an external time-dependent field. This more closely reflects the experimental conditions. A six-dimensional dipole surface is computed. The multiconfiguration time-dependent Hartree method is exploited to propagate the corresponding six-dimensional wave packets. Special emphasis is placed on the excitation of the out-of-plane bending vibration and on the dissociation of the molecule. In the case of DFCO, we predict that it is possible to excite the out-of-plane bending mode of vibration and to drive the dissociation to DF+CO with only one laser pulse with a fixed frequency and without excitation of an electronic state.
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33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
33.15.Mt Rotation, vibration, and vibration-rotation constants
31.15.xr Self-consistent-field methods
33.80.Gj Diffuse spectra; predissociation, photodissociation

An ab initio calculation of the vibronic energy levels of the X 2Π and 1 2Δ electronic states of C2P

Stanka Jerosimić and Miljenko Perić

J. Chem. Phys. 129, 144305 (2008); http://dx.doi.org/10.1063/1.2991414 (6 pages) | Cited 2 times

Online Publication Date: 10 October 2008

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In the present study, the results of an ab initio calculation of the vibronic energy levels in the X 2Π and 1 2Δ electronic states of C2P are reported. This work is motivated by recent measurements carried out by [ Sunahori et al. J. Chem. Phys. 128, 244311 (2008) ]. The vertical electronic spectrum, excitation energies, bending potential curves, and spin-orbit constants for the title molecule are computed by means of the state-average complete active space self-consistent field and multireference configuration interaction approach. Vibronic energy levels of the X 2Π and 1 2Δ states are calculated with the help of a simple, effectively one-dimensional model. The results of the present study strongly support the analysis of experimental data by Sunahori et al. and offer reliable predictions for experimental searches for heretofore unobserved electronic states.
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33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
31.50.Df Potential energy surfaces for excited electronic states
31.15.xr Self-consistent-field methods
31.15.am Relativistic configuration interaction (CI) and many-body perturbation calculations
33.15.Bh General molecular conformation and symmetry; stereochemistry
31.15.aj Relativistic corrections, spin-orbit effects, fine structure; hyperfine structure

Experimental interrogation of the multidimensional He+ICl(E,v†) and He+ICl(β,v†) intermolecular potential energy surfaces

Joshua P. Darr and Richard A. Loomis

J. Chem. Phys. 129, 144306 (2008); http://dx.doi.org/10.1063/1.2990661 (11 pages) | Cited 6 times

Online Publication Date: 10 October 2008

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Resonant two-photon excitation of the T-shaped and linear He⋯I35Cl(X,v″ = 0) complexes is used to access the intermolecular vibrational levels bound within the He+ICl(β,v† = 0–2) and He+ICl(E,v† = 11,12) intermolecular potentials. The excitation utilizes different metastable intermolecular vibrational levels within the He+ICl(A,v′ = 15) and He+ICl(B,v′ = 2,3) potentials to access levels with varying intermolecular vibrational excitation in the ion-pair states. In addition to providing data revealing properties of the He+ICl(E,v†) and He+ICl(β,v†) potentials, the transition energies of the observed features permit the relative binding energies of the T-shaped and linear ground-state He⋯ICl(X,v″ = 0) conformers to be accurately measured. The binding energies of the T-shaped and linear He⋯I35Cl(X,v″ = 0) conformers are 16.6(3) and 22.0(2) cm−1, respectively. These values and the observed transition energies are then used to set the binding energies of the T-shaped He⋯I35Cl complexes in the He+ICl(A,v′ = 15), He+ICl(B,v′ = 3), He+ICl(β,v† = 1), and He+ICl(E,v† = 12) potentials as 13.4(3), 13.3(3), 41(1), and 39.2(4) cm−1, respectively. Nonadiabatic coupling between specific intermolecular vibrational levels within the He+ICl(β,v†) state and the ICl(D′,v†) molecular state is observed.
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51.70.+f Optical and dielectric properties
34.20.Gj Intermolecular and atom-molecule potentials and forces
34.50.Ez Rotational and vibrational energy transfer
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy

The mechanism of paramagnetic NMR relaxation produced by Mn(II): Role of orthorhombic and fourth-order zero field splitting terms

Robert Sharp

J. Chem. Phys. 129, 144307 (2008); http://dx.doi.org/10.1063/1.2981565 (10 pages) | Cited 1 time

Online Publication Date: 10 October 2008

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Mn(II) is a spin-5/2 paramagnetic ion that mediates a characteristically large NMR paramagnetic relaxation enhancement (NMR-PRE) of nuclear spins in solution. In the range of high magnetic field strengths (above about 0.3 T), where the electronic Zeeman interaction provides the largest term of the electron spin Hamiltonian, NMR relaxation mechanism is well understood. In the lower field range, the physical picture is more complex because of the presence in the spin Hamiltonian of zero field splitting (ZFS) terms that are comparable to or greater than the Zeeman term. This work describes a systematic study of the relaxation mechanism in the low field range, particularly aspects involving the dependence of NMR-PRE on the orthorhombic (E) and fourth-order (aq(4), q = 0,2,4) ZFS tensor components. It is shown that the fourfold (a4(4)) and twofold (a2(4)) fourth-order components exert large orientation-dependent influences on the NMR-PRE. Thus, fourth-order terms with magnitudes equal to only a few percent of the quadratic ZFS terms (D,E) produce large changes in the shape of the magnetic field profile of the PRE. Effects arising from the orthorhombic quadratic ZFS term (E) are much smaller than those of the fourth-order terms and can in most cases be neglected. However, effects due to a4(4) and a2(4) need to be included in simulations of low field data.
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33.25.+k Nuclear resonance and relaxation
33.57.+c Magneto-optical and electro-optical spectra and effects

On the origin of the large electron correlation contribution to the hyperpolarizabilities of some diacetylene rare gas compounds

Tadeusz Pluta, Aggelos Avramopoulos, Manthos G. Papadopoulos, and Jerzy Leszczynski

J. Chem. Phys. 129, 144308 (2008); http://dx.doi.org/10.1063/1.2987303 (6 pages) | Cited 2 times

Online Publication Date: 10 October 2008

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A comprehensive study of the linear and nonlinear molecular optical properties of HRgC4H, where Rg = Ar,Kr,Xe, has been performed. Dynamical electron correlation effects were computed by employing the coupled cluster methodology. A large electron correlation contribution to the nonlinear properties of HArC4H has been revealed. This contribution decreases by increasing the atomic number of the inserted rare gas atom. In order to interpret the origin of this noteworthy property, the complete active space self-consistent field method was employed. We have performed a systematic study of the linear and nonlinear electric properties by modifying the active space. The calculations have shown the significant contribution of the doubly excited σ*2 configuration and a negligible contribution of π*2. A quite remarkable discrepancy between numerically and analytically evaluated hyperpolarizabilities has also been observed for HArC4H. This was attributed to the contribution of near degenerate states.
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31.15.vj Electron correlation calculations for atoms and ions: excited states
31.15.bw Coupled-cluster theory
33.15.Bh General molecular conformation and symmetry; stereochemistry
31.15.xr Self-consistent-field methods
42.65.-k Nonlinear optics

Atomistic dipole moments and polarizabilities of NaN clusters, N = 2–20

K. Jackson, L. Ma, M. Yang, and J. Jellinek

J. Chem. Phys. 129, 144309 (2008); http://dx.doi.org/10.1063/1.2978169 (10 pages) | Cited 8 times

Online Publication Date: 13 October 2008

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The atomic-level response of NaN clusters, N = 2–20, to a small static external electric field is studied using a method that decomposes the total cluster dipole moment and polarizability into contributions from nonoverlapping atomic volumes. The atomic dipole moments and polarizabilities are, in turn, partitioned into the so-called dipole and charge-transfer components. The former characterizes a dielectric type of a response, whereas the latter represents a metallic type of a response. Analysis of the atomic polarizabilities points to their strong dependence on the site, or location, of the atoms within the structure of the clusters. Surface atoms have larger polarizabilities than the interior ones. Overall, the fraction of the charge-transfer component of the averaged atomic polarizabilities is an increasing function of the cluster size. The charge-transfer component is also responsible for the structure/shape driven variations in the atomic polarizabilities. The anisotropy of the total polarizabilities correlates with the shape anisotropy of the clusters.
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36.40.Mr Spectroscopy and geometrical structure of clusters
34.70.+e Charge transfer
32.30.-r Atomic spectra
36.40.Wa Charged clusters

Temperature and isotope effects on water cluster ions with path integral molecular dynamics based on the fourth order Trotter expansion

Kimichi Suzuki, Motoyuki Shiga, and Masanori Tachikawa

J. Chem. Phys. 129, 144310 (2008); http://dx.doi.org/10.1063/1.2987445 (8 pages) | Cited 12 times

Online Publication Date: 13 October 2008

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Path integral molecular dynamics simulation based on the fourth order Trotter expansion has been performed to elucidate the geometrical isotope effect of water dimer anions, H3O2−, D3O2−, and T3O2−, at different temperatures from 50 to 600 K. At low temperatures below 200 K the hydrogen-bonded hydrogen nucleus is near the center of two oxygen atoms with mostly O⋯X⋯O geometry (where X = H, D, or T), while at high temperatures above 400 K, hydrogen becomes more delocalized, showing the coexistence between O⋯X–O and O–X⋯O. The OO distance tends to be shorter as the isotopomer is heavier at low temperatures, while this ordering becomes opposite at high temperatures. It is concluded that the coupling between the OO stretching mode and proton transfer modes is a key to understand such a temperature dependence of a hydrogen-bonded structure.
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36.40.Mr Spectroscopy and geometrical structure of clusters

Rotational spectroscopic study of carbonyl sulfide solvated with hydrogen molecules

Julie M. Michaud and Wolfgang Jäger

J. Chem. Phys. 129, 144311 (2008); http://dx.doi.org/10.1063/1.2976167 (11 pages) | Cited 4 times

Online Publication Date: 14 October 2008

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Rotational spectra of small-sized (H2)N-OCS clusters with N = 2–7 were measured using a pulsed-jet Fourier transform microwave spectrometer. These include spectra of pure (para-H2)N-OCS clusters, pure (ortho-H2)N-OCS clusters, and mixed ortho-H2 and para-H2 containing clusters. The rotational lines of ortho-H2 molecules containing clusters show proton spin-proton spin hyperfine structure, and the pattern evolves as the number of ortho-H2 molecules in the cluster increases. Various isotopologues of the clusters were investigated, including those with O13CS, OC33S, OC34S, and O13C34S. Nuclear quadrupole hyperfine structures of rotational transitions were observed for 33S (nuclear spin quantum number I = 3/2) containing isotopologues. The 33S nuclear quadrupole coupling constants are compared to the corresponding constant of the OCS monomer and those of the HeN-OCS clusters. The assignment of the number of solvating hydrogen molecules N is supported by the analyses of the proton spin-proton spin hyperfine structures of the mixed clusters, the dependence of line intensities on sample conditions (pressure and concentrations), and the agreement of the (para-H2)N-OCS and (ortho-H2)N-OCS rotational constants with those from a previous infrared study [ J. Tang and A. R. W. McKellar, J. Chem. Phys. 121, 3087 (2004) ].
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33.20.Sn Rotational analysis
33.15.Pw Fine and hyperfine structure
33.20.Ea Infrared spectra
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
back to top Condensed Phase Dynamics, Structure, and Thermodynamics: Spectroscopy, Reactions, and Relaxation

On the accuracy of predicting shear viscosity of molecular liquids using the periodic perturbation method

Lifeng Zhao, Tao Cheng, and Huai Sun

J. Chem. Phys. 129, 144501 (2008); http://dx.doi.org/10.1063/1.2936986 (9 pages) | Cited 2 times

Online Publication Date: 8 October 2008

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Non-equilibrium molecular dynamics simulations are performed to calculate shear viscosities of 16 representative molecular liquids using the periodic perturbation method (PPM). A perturbation index is defined to measure the strength of the perturbation. It is identified that the predictions are systematically underestimated using PPM. The origin of the underestimate is the acoustic wave in the liquid density, which is persistent in the simulation box unless the perturbation is completely removed. However, there is a linear correlation between the perturbation indexes and the apparent viscosities, which can be utilized to accurately predict the shear viscosities. Finally, it is demonstrated that general force fields derived based on equilibrium properties can be used to predict the shear viscosities of small molecular liquids with relative errors less than 10%.
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66.20.-d Viscosity of liquids; diffusive momentum transport
61.25.Em Molecular liquids
61.20.Ja Computer simulation of liquid structure
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