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14 Jan 2011

Volume 134, Issue 2, Articles (02xxxx)

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J. Chem. Phys. 134, 024501 (2011); http://dx.doi.org/10.1063/1.3514149 (7 pages)

Silvio a Beccara, Pietro Faccioli, Marcello Sega, Francesco Pederiva, Giovanni Garberoglio, and Henri Orland
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Communication: A dramatic transition from nonferromagnet to ferromagnet in finite fused-azulene chain

Zexing Qu, Shushu Zhang, Chungen Liu, and Jean-Paul Malrieu

J. Chem. Phys. 134, 021101 (2011); http://dx.doi.org/10.1063/1.3533363 (4 pages)

Online Publication Date: 14 January 2011

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One-dimensional fused-azulene oligomers (n = 2 − 6) are studied with the effective valence bond as well as density functional theory methods. A nonferromagnetic (closed-shell singlet) to ferromagnetic (triplet) ground state transformation is witnessed with increasing length of oligomers. The computational results are interpreted in terms of spin coupling between the unpaired electrons of two nonbonding molecular orbitals localized, respectively, on the top and bottom chains of the oligomers. The present study provides a theoretical suggestion for understanding the ferromagnetic spin polarizations that has been observed very recently in graphene nanoribbons.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.20.Rv Polymers and organic compounds
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The use of two-phase molecular dynamics simulations to determine the phase behavior and critical point of propane molecular models

Sonal Patel, W. Vincent Wilding, and Richard L. Rowley

J. Chem. Phys. 134, 024101 (2011); http://dx.doi.org/10.1063/1.3528117 (8 pages) | Cited 1 time

Online Publication Date: 10 January 2011

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Molecular dynamics simulations were performed to determine two-phase configurations of model propane molecules below the critical point and in the near-critical, two-phase region. A postprocessor that uses a Monte Carlo method for determination of volumes attributable to each molecule was used to obtain density histograms of the particles from which the bulk coexisting equilibrium vapor and liquid densities were determined. This method of analyzing coexisting densities in a two-phase simulation is straightforward and can be easily implemented for complex, multisite models. Various degrees of internal flexibility in the propane models have little effect on the coexisting densities at temperatures 40 K or more below the critical point, but internal flexibility (angle bending and bond vibrations) does affect the saturated liquid densities in the near-critical region, changing the critical temperature by approximately 20 K. Shorter cutoffs were also found to affect the phase dome and the location of the critical point.
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61.20.Ja Computer simulation of liquid structure
64.60.F- Equilibrium properties near critical points, critical exponents

Regarding the validity of the time-dependent Kohn–Sham approach for electron-nuclear dynamics via trajectory surface hopping

Sean A. Fischer, Bradley F. Habenicht, Angeline B. Madrid, Walter R. Duncan, and Oleg V. Prezhdo

J. Chem. Phys. 134, 024102 (2011); http://dx.doi.org/10.1063/1.3526297 (9 pages) | Cited 1 time

Online Publication Date: 10 January 2011

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The implementation of fewest-switches surface-hopping (FSSH) within time-dependent Kohn–Sham (TDKS) theory [Phys. Rev. Lett. 95, 163001 (2005)] has allowed us to study successfully excited state dynamics involving many electronic states in a variety of molecular and nanoscale systems, including chromophore–semiconductor interfaces, semiconductor and metallic quantum dots, carbon nanotubes and graphene nanoribbons, etc. At the same time, a concern has been raised that the KS orbital basis used in the calculation provides only approximate potential energy surfaces [J. Chem. Phys. 125, 014110 (2006)]. While this approximation does exist in our method, we show here that FSSH-TDKS is a viable option for computationally efficient calculations in large systems with straightforward excited state dynamics. We demonstrate that the potential energy surfaces and nonadiabatic transition probabilities obtained within the TDKS and linear response (LR) time-dependent density functional theories (TDDFT) agree semiquantitatively for three different systems, including an organic chromophore ligating a transition metal, a quantum dot, and a small molecule. Further, in the latter case the FSSH-TDKS procedure generates results that are in line with FSSH implemented within LR-TDDFT. The FSSH-TDKS approach is successful for several reasons. First, single-particle KS excitations often give a good representation of LR excitations. In this regard, DFT compares favorably with the Hartree–Fock theory, for which LR excitations are typically combinations of multiple single-particle excitations. Second, the majority of the FSSH-TDKS applications have been performed with large systems involving simple excitations types. Excitation of a single electron in such systems creates a relatively small perturbation to the total electron density summed over all electrons, and it has a small effect on the nuclear dynamics compared, for instance, with thermal nuclear fluctuations. In such cases an additional, classical-path approximation can be made. Third, typical observables measured in time-resolved experiments involve averaging over many initial conditions. Such averaging tends to cancel out random errors that may be encountered in individual simulated trajectories. Finally, if the flow of energy between electronic and nuclear subsystems is insignificant, the ad hoc FSSH procedure is not required, and a straightforward mean-field, Ehrenfest approach is sufficient. Then, the KS representation provides rigorously a convenient and efficient basis for numerically solving the TDDFT equations of motion.
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73.20.At Surface states, band structure, electron density of states
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
73.21.La Quantum dots
73.22.Pr Electronic structure of graphene
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Vibrational transitions of the 7LiH+ ion calculated without the Born–Oppenheimer approximation and with leading relativistic corrections

Sergiy Bubin, Monika Stanke, and Ludwik Adamowicz

J. Chem. Phys. 134, 024103 (2011); http://dx.doi.org/10.1063/1.3525679 (4 pages)

Online Publication Date: 11 January 2011

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We recently presented very accurate calculations of the fundamental vibrational frequency of the 7LiH+ and 3He4He+ ions [Stanke et al. Phys. Rev. A 79, 060501(R) (2009)] performed without the Born–Oppenheimer approximation and included leading relativistic corrections. The accuracy of those calculations was estimated to be of the order of 0.06 cm−1. In the present work we extend the calculations to the remaining pure vibrational states of 7LiH+ and similarly accurate results are generated. They may lead to the experimental search for still unidentified lines corresponding to those transitions.
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31.30.J- Relativistic and quantum electrodynamic (QED) effects in atoms, molecules, and ions
33.20.Tp Vibrational analysis

Visualizing electron correlation by means of ab initio scanning tunneling spectroscopy images of single molecules

Dimitrios Toroz, Massimo Rontani, and Stefano Corni

J. Chem. Phys. 134, 024104 (2011); http://dx.doi.org/10.1063/1.3520567 (11 pages)

Online Publication Date: 11 January 2011

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Scanning tunneling microscopy (STM) has been a fundamental tool to characterize many-body effects in condensed matter systems, from extended solids to quantum dots. STM of molecules decoupled from the supporting conductive substrate has the potential to extend STM characterization of many-body effects to the molecular world as well. In this paper, we describe a many-body tunneling theory for molecules decoupled from the STM substrate, and we report on the use of standard quantum chemical methods to calculate the quantities necessary to provide the “correlated” STM molecular image. The developed approach has been applied to 18 different molecules to explore the effects of their chemical nature and of their substituents, as well as to verify the possible contribution by transition metal centers. Whereas the bulk of calculations has been performed with the configuration interaction method with single and double excitations (CISD), because of the computational cost some tests have been also performed with the more accurate coupled cluster with single and double excitations (CCSD) method to quantify the importance of the computational level on many-body STM images. We have found that correlation induces a remarkable squeezing of the images, and that correlated images are not derived from Hartree–Fock HOMO or LUMO alone, but include contributions from other orbitals as well. Although correlation effects are too small to be resolved by present STM experiments for the studied molecules, our results provide hints for seeking out other species with larger, and possibly experimentally detectable, correlation effects.
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82.37.Gk STM and AFM manipulations of a single molecule
68.43.Mn Adsorption kinetics
82.20.Sb Correlation function theory of rate constants and its applications

A new approach to decoherence and momentum rescaling in the surface hopping algorithm

Joseph E. Subotnik and Neil Shenvi

J. Chem. Phys. 134, 024105 (2011); http://dx.doi.org/10.1063/1.3506779 (19 pages) | Cited 9 times

Online Publication Date: 11 January 2011

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As originally proposed, the fewest switches surface hopping (FSSH) algorithm does not allow for decoherence between wavefunction amplitudes on different adiabatic surfaces. In this paper, we propose an inexpensive correction to standard FSSH dynamics wherein we explicitly model the decoherence of nuclear wave packets on distinct electronic surfaces. Our augmented fewest switches surface hopping approach is conceptually simple and, thus far, it has allowed us to capture several key features of the exact quantum results. Two points in particular merit attention. First, we obtain the correct branching ratios when a quantum particle passes through more than one region of nonadiabatic coupling. Second, our formalism provides a new and natural approach for rescaling nuclear momenta after a surface hop. Both of these features should become increasingly important as surface hopping schemes are applied to higher-dimensional problems.
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73.25.+i Surface conductivity and carrier phenomena
73.20.At Surface states, band structure, electron density of states

Autoionization widths by Stieltjes imaging applied to Lanczos pseudospectra

S. Kopelke, K. Gokhberg, L. S. Cederbaum, F. Tarantelli, and V. Averbukh

J. Chem. Phys. 134, 024106 (2011); http://dx.doi.org/10.1063/1.3523982 (7 pages) | Cited 1 time

Online Publication Date: 11 January 2011

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Excited states of atoms and molecules lying above the ionization threshold can decay by electron emission in a process commonly known as autoionization. The autoionization widths can be calculated conveniently using Fano formalism and discretized atomic and molecular spectra by a standard procedure referred to as Stieltjes imaging. The Stieltjes imaging procedure requires the use of the full discretized spectrum of the final states of the autoionization, making its use for poly-atomic systems described by high-quality basis sets impractical. Following our previous work on photoionization cross-sections, here we show that also in the case of autoionization widths, the full diagonalization bottleneck can be overcome by the use of Lanczos pseudospectra. We test the proposed method by calculating the well-documented autoionization widths of inner-valence-excited neon and apply the new technique to autoionizing states of hydrofluoric acid and benzene.
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32.80.Zb Autoionization
32.80.Fb Photoionization of atoms and ions
33.80.Eh Autoionization, photoionization, and photodetachment
33.60.+q Photoelectron spectra

Potential curves for inner-shell states of CO calculated at multiconfigurational self-consistent field level

Alexandre B. Rocha

J. Chem. Phys. 134, 024107 (2011); http://dx.doi.org/10.1063/1.3528725 (5 pages) | Cited 2 times

Online Publication Date: 11 January 2011

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A general strategy to calculate potential curves at multiconfigurational self-consistent field (MCSCF) level for inner-shell states is reported in this paper. Convergence is commonly very tough for inner-shell states, especially at this level of calculation, due to the problem of variational collapse of the inner-shell wave function to the ground or to a low-lying excited state. The present method allows to avoid this drawback by a sequence of constrained optimization in the orbital mixing step. The specific states studied are that resulting from transitions X 1Σ+ → (C 1s−1 π*) 1,3Π of CO. Accurate values are achieved for transition energies and vibrational splittings. A comparison is made with other approach, i.e., inner-shell CI based on a MCSCF wave function optimized for ground or low-lying excited states. This last approach is shown to fail in describing the whole potential curve.
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31.15.xr Self-consistent-field methods
31.50.Df Potential energy surfaces for excited electronic states
33.20.Tp Vibrational analysis

Performance of dynamically weighted multiconfiguration self-consistent field and spin-orbit coupling calculations of diatomic molecules of Group 14 elements

Tao Zeng, Dmitri G. Fedorov, and Mariusz Klobukowski

J. Chem. Phys. 134, 024108 (2011); http://dx.doi.org/10.1063/1.3529840 (11 pages)

Online Publication Date: 11 January 2011

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The efficacy of several multiconfiguration self-consistent field (MCSCF) methods in the subsequent spin-orbit coupling calculations was studied. Three MCSCF schemes to generate molecular orbitals were analyzed: state-specific, state-averaged, and dynamically weighted MCSCF. With Sn2+ as the representative case, we show that the state-specific MCSCF orbitals lead to discontinuities in potential energy curves when avoided crossings of electronic states occur; this problem can be solved using the state-averaged or dynamically weighted MCSCF orbitals. The latter two schemes are found to give similar results when dynamic electron correlation is considered, which we calculated at the level of multiconfigurational quasidegenerate perturbation theory (MCQDPT). We employed the recently developed Douglas–Kroll spin-orbit adapted model core potential, ZFK3-DK3, and the dynamically weighted MCSCF scheme to calculate the spectroscopic constants of the mono-hydrides and compared them to the results obtained using the older set of potentials, MCP-TZP. We also showed that the MCQDPT tends to underestimate the dissociation energies of the hydrides and discussed to what extent coupled-cluster theory can be used to improve results.
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31.15.xr Self-consistent-field methods
31.15.bw Coupled-cluster theory
33.15.Fm Bond strengths, dissociation energies
31.15.xp Perturbation theory
31.15.am Relativistic configuration interaction (CI) and many-body perturbation calculations
31.50.-x Potential energy surfaces

Simple and effective application of the Wang–Landau method for multicanonical molecular dynamics simulation

Hiromitsu Shimoyama, Haruki Nakamura, and Yasushige Yonezawa

J. Chem. Phys. 134, 024109 (2011); http://dx.doi.org/10.1063/1.3517105 (5 pages)

Online Publication Date: 11 January 2011

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We propose a novel application of the Wang–Landau method (WLM) for multicanonical molecular dynamics (McMD) simulations. Originally, WLM was developed for Monte Carlo (MC) simulations. Fundamentally, WLM remarkably reduces simulation efforts because it estimates the optimal multicanonical energy function automatically. When WLM is applied to McMD, not only the multicanonical energy but also energy gradient must be estimated adequately. However, because of the rugged multicanonical energy function at the early simulation stage, applications of WLM for MD simulations are difficult and require a smoothing procedure: simulation efforts such as cubic-spline extrapolation and gathering multiple preruns are utilized for smoothing. We propose a simple and effective smoothing method that requires only one additional equation and two time-dependent parameters. As a result, our method produced the correct multicanonical energy function and succeeded in the flat sampling of a small biomolecule with reduced simulation effort.
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87.15.ak Monte Carlo simulations
87.14.E- Proteins

Shape transformation of lipid vesicles induced by diffusing macromolecules

W. T. Góźdź

J. Chem. Phys. 134, 024110 (2011); http://dx.doi.org/10.1063/1.3530069 (8 pages)

Online Publication Date: 11 January 2011

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The attachment of macromolecules to the surface of a lipid vesicle may cause its deformations such as budding or creation of cylindrical protrusions. Diffusion of the macromolecules in the membranes may cause its shape transformations. The process of shrinking the protrusions due to diffusion of the macromolecules is investigated. It is assumed that macromolecules modify locally the spontaneous curvature and bending rigidity of the lipid membrane. Both spontaneous curvature and bending rigidities depend on the concentration of membrane components. It has been shown that cylindrical protrusions are created when the macromolecules which induce large spontaneous curvature are accumulated at a piece of the vesicle surface. It has been observed that here the elastic constants influence very little the evolution of the vesicle shape caused by diffusing macromolecules and the most important is the value the spontaneous curvature imposed by the macromolecules.
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87.16.dp Transport, including channels, pores, and lateral diffusion
82.39.Wj Ion exchange, dialysis, osmosis, electro-osmosis, membrane processes
87.14.Cc Lipids
87.15.Vv Diffusion
87.17.Rt Cell adhesion and cell mechanics
82.30.Nr Association, addition, insertion, cluster formation

Estimating equilibrium ensemble averages using multiple time slices from driven nonequilibrium processes: Theory and application to free energies, moments, and thermodynamic length in single-molecule pulling experiments

David D. L. Minh and John D. Chodera

J. Chem. Phys. 134, 024111 (2011); http://dx.doi.org/10.1063/1.3516517 (9 pages) | Cited 2 times

Online Publication Date: 12 January 2011

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Recently discovered identities in statistical mechanics have enabled the calculation of equilibrium ensemble averages from realizations of driven nonequilibrium processes, including single-molecule pulling experiments and analogous computer simulations. Challenges in collecting large data sets motivate the pursuit of efficient statistical estimators that maximize use of available information. Along these lines, Hummer and Szabo developed an estimator that combines data from multiple time slices along a driven nonequilibrium process to compute the potential of mean force. Here, we generalize their approach, pooling information from multiple time slices to estimate arbitrary equilibrium expectations. Our expression may be combined with estimators of path-ensemble averages, including existing optimal estimators that use data collected by unidirectional and bidirectional protocols. We demonstrate the estimator by calculating free energies, moments of the polymer extension, the thermodynamic metric tensor, and the thermodynamic length in a model single-molecule pulling experiment. Compared to estimators that only use individual time slices, our multiple time-slice estimators yield substantially smoother estimates and achieve lower variance for higher-order moments.
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36.20.Ey Conformation (statistics and dynamics)
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility

A study of electron affinities using the initiator approach to full configuration interaction quantum Monte Carlo

D. M. Cleland, George H. Booth, and Ali Alavi

J. Chem. Phys. 134, 024112 (2011); http://dx.doi.org/10.1063/1.3525712 (9 pages) | Cited 1 time

Online Publication Date: 13 January 2011

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For the atoms with Z ⩽ 11, energies obtained using the “initiator” extension to full configuration interaction quantum Monte Carlo (i-FCIQMC) come to within statistical errors of the FCIQMC results. As these FCIQMC values have been shown to converge onto FCI results, the i-FCIQMC method allows similar accuracy to be achieved while significantly reducing the scaling with the size of the Slater determinant space. The i-FCIQMC electron affinities of the Z ⩽ 11 atoms in the aug-cc-pVXZ basis sets are presented here. In every case, values are obtained to well within chemical accuracy [the mean absolute deviation (MAD) from the relativistically corrected experimental values is 0.41 mEh], and significantly improve on coupled cluster with singles, doubles and perturbative triples [CCSD(T)] results. Since the only remaining source of error is basis set incompleteness, we have investigated using CCSD(T)-F12 contributions to correct the i-FCIQMC results. By doing so, much faster convergence with respect to basis set size may be achieved for both the electron affinities and the FCIQMC ionization potentials presented in a previous paper. With this F12 correction, the MAD can be further reduced to 0.13 mEh for the electron affinities and 0.31 mEh for the ionization potentials.
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31.15.bw Coupled-cluster theory
32.50.+d Fluorescence, phosphorescence (including quenching)
31.30.jc Relativistic corrections to atomic structure and properties
31.15.am Relativistic configuration interaction (CI) and many-body perturbation calculations

Single center method: A computational tool for ionization and electronic excitation studies of molecules

Ph. V. Demekhin, A. Ehresmann, and V. L. Sukhorukov

J. Chem. Phys. 134, 024113 (2011); http://dx.doi.org/10.1063/1.3526026 (11 pages) | Cited 1 time

Online Publication Date: 13 January 2011

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We discuss the recent progress in the development of the single center (SC) method for computation of highly-delocalized discrete and partial photoelectron wave continuous functions of molecules. Basic equations of the SC method are presented, and an efficient scheme for the numerical solution of a system of coupled Hartree–Fock equations for a photoelectron is described. Several illustrative applications of the method to photoionization and electronic excitation processes in diatomic molecules are considered. Thereby, we demonstrate its potential for theoretically studying angularly resolved molecular photoionization processes.
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33.80.Eh Autoionization, photoionization, and photodetachment
33.60.+q Photoelectron spectra
31.15.xr Self-consistent-field methods

Excitation energy calculation of conjugated hydrocarbons: A new Pariser–Parr–Pople model parameterization approaching CASPT2 accuracy

Dawei Zhang, Zexing Qu, Chungen Liu, and Yuansheng Jiang

J. Chem. Phys. 134, 024114 (2011); http://dx.doi.org/10.1063/1.3526066 (10 pages) | Cited 2 times

Online Publication Date: 13 January 2011

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A new parameterization for the Pariser–Parr–Pople (PPP) model for conjugated hydrocarbons is proposed in this work. The distance-dependence of PPP parameters are obtained from CASPT2 ground state and low-lying excited state energies of ethylene and its cation at various C–C single bond lengths and are fitted to a set of carefully chosen mathematical functions. Our new PPP model is applied to the calculation of vertical singlet–triplet energy gaps and the excitation energies for low-lying π→π* valence excitations in various π-conjugated molecules. Results with the new PPP model are consistently better than the standard PPP model in use. It often surpasses density functional theory and single-reference excited state methods such as configuration interaction singles or time-dependent density functional theory in terms of its accuracy and agrees reasonably well with high-level theories or experiments.
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31.15.bu Semi-empirical and empirical calculations (differential overlap, Hückel, PPP methods, etc.)
33.15.Dj Interatomic distances and angles
31.15.xr Self-consistent-field methods
31.15.xp Perturbation theory

Turning symmetric an asymmetric hydrogen bond with the inclusion of nuclear quantum effects: The case of the [CN···H···NC]− complex

Diego V. Moreno, Sergio A. González, and Andrés Reyes

J. Chem. Phys. 134, 024115 (2011); http://dx.doi.org/10.1063/1.3521272 (7 pages)

Online Publication Date: 13 January 2011

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Nuclear quantum effects (NQE) on the geometry, energy, and electronic structure of the [CN·L·NC]− complex (L = H, D, T) are investigated with the recently developed APMO/MP2 code. This code implements the nuclear molecular orbital approach (NMO) at the Hartree–Fock (HF) and MP2 levels of theory for electrons and quantum nuclei. In a first study, we examined the H/D/T isotope effects on the geometry and electronic structure of the CNH molecule at NMO/HF and NMO/MP2 levels of theory. We found that when increasing the hydrogen nuclear mass there is a reduction of the RN-H bond distance and an increase of the electronic population on the hydrogen atom. Our calculated bond distances are in good agreement with experimental and other theoretical results. In a second investigation, we explored the hydrogen NQE on the geometry of [CNHNC]− complex at the NMO/HF and NMO/MP2 levels of theory. We discovered that while a NMO/HF calculation presented an asymmetric hydrogen bond, the NMO/MP2 calculation revealed a symmetric H-bond. We also examined the H/D/T isotope effects on the geometry and stabilization energy of the [CNHNC]− complex. We noted that gradual increases in hydrogen mass led to reductions of the RNN distance and destabilization of the hydrogen bond (H-bond). A discussion of these results is given in terms of the hydrogen nuclear delocalization effects on the electronic structure and energy components. To the best of our knowledge, this is the first ab initio NMO study that reveals the importance of including nuclear quantum effects in conventional electronic structure calculations for an enhanced description of strong-low-barrier H-bonded systems.
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31.15.ae Electronic structure and bonding characteristics
31.30.Gs Hyperfine interactions and isotope effects
33.15.Dj Interatomic distances and angles
31.15.xr Self-consistent-field methods
33.15.Fm Bond strengths, dissociation energies
33.15.Bh General molecular conformation and symmetry; stereochemistry

Improved hybrid functional for solids: The HSEsol functional

Laurids Schimka, Judith Harl, and Georg Kresse

J. Chem. Phys. 134, 024116 (2011); http://dx.doi.org/10.1063/1.3524336 (11 pages) | Cited 4 times

Online Publication Date: 13 January 2011

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We introduce the hybrid functional HSEsol. It is based on PBEsol, a revised Perdew–Burke–Ernzerhof functional, designed to yield accurate equilibrium properties for solids and their surfaces. We present lattice constants, bulk moduli, atomization energies, heats of formation, and band gaps for extended systems, as well as atomization energies for the molecular G2-1 test set. Compared to HSE, significant improvements are found for lattice constants and atomization energies of solids, but atomization energies of molecules are slightly worse than for HSE. Additionally, we present zero-point anharmonic expansion corrections to the lattice constants and bulk moduli, evaluated from ab initio phonon calculations.
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61.50.-f Structure of bulk crystals
71.15.-m Methods of electronic structure calculations
82.60.Cx Enthalpies of combustion, reaction, and formation
81.40.Jj Elasticity and anelasticity, stress-strain relations
82.60.Hc Chemical equilibria and equilibrium constants

Broadband inversion for MAS NMR with single-sideband-selective adiabatic pulses

Andrew J. Pell, Gwendal Kervern, Lyndon Emsley, Michaël Deschamps, Dominique Massiot, Philip J. Grandinetti, and Guido Pintacuda

J. Chem. Phys. 134, 024117 (2011); http://dx.doi.org/10.1063/1.3521491 (13 pages) | Cited 1 time

Online Publication Date: 13 January 2011

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We explain how and under which conditions it is possible to obtain an efficient inversion of an entire sideband family of several hundred kHz using low-power, sideband-selective adiabatic pulses, and we illustrate with some experimental results how this framework opens new avenues in solid-state NMR for manipulating spin systems with wide spinning-sideband (SSB) manifolds. This is achieved through the definition of the criteria of phase and amplitude modulation for designing an adiabatic inversion pulse for rotating solids. In turn, this is based on a framework for representing the Hamiltonian of the spin system in an NMR experiment under magic angle spinning (MAS). Following earlier ideas from Caravatti et al. [J. Magn. Reson. 55, 88 (1983)], the so-called “jolting frame” is used, which is the interaction frame of the anisotropic interaction giving rise to the SSB manifold. In the jolting frame, the shift modulation affecting the nuclear spin is removed, while the Hamiltonian corresponding to the RF field is frequency modulated and acquires a spinning-sideband pattern, specific for each crystallite orientation.
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76.60.-k Nuclear magnetic resonance and relaxation
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.10.Dg Crystal-field theory and spin Hamiltonians
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.30.Sg Magnetocaloric effect, magnetic cooling

Open-system electronic dynamics and thermalized electronic structure

Craig T. Chapman, Wenkel Liang, and Xiaosong Li

J. Chem. Phys. 134, 024118 (2011); http://dx.doi.org/10.1063/1.3526027 (6 pages) | Cited 2 times

Online Publication Date: 14 January 2011

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We propose and implement a novel computational method for simulating open-system electronic dynamics and obtaining thermalized electronic structures within an open quantum system framework. The system–bath interaction equation of motion is derived and modeled from the local harmonic oscillator description for electronic density change. The nonequilibrium electronic dynamics in a thermal bath is simulated using first-order kinetics. The resultant electronic densities are temperature-dependent and can take characteristics of the ground and excited states. We present results of calculations performed on H2 and 1,3-butadiene performed at the Hartree–Fock level of theory using a minimal Slater-type orbital basis set.
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31.30.J- Relativistic and quantum electrodynamic (QED) effects in atoms, molecules, and ions
31.15.xr Self-consistent-field methods

Monomer density profiles for polymer chains in confined geometries: Massive field theory approach

Z. Usatenko

J. Chem. Phys. 134, 024119 (2011); http://dx.doi.org/10.1063/1.3529426 (10 pages)

Online Publication Date: 14 January 2011

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Taking into account the well known correspondence between the field theoretical φ4 O(n)-vector model in the limit n → 0 and the behavior of long flexible polymer chains in a good solvent, the universal density–force relation is analyzed and the corresponding universal amplitude ratio B real is obtained using the massive field theory approach in fixed space dimensions d < 4. The monomer density profiles of ideal chains and real polymer chains with excluded volume interaction in a good solvent between two parallel repulsive walls, one repulsive and one inert wall, are obtained in the framework of the massive field theory approach up to one-loop order. Besides, the monomer density profiles for the dilute polymer solution confined in semi-infinite space containing mesoscopic spherical particle of big radius are calculated. The obtained results are in qualitative agreement with previous theoretical investigations and with the results of Monte Carlo simulations.
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61.25.he Polymer solutions
61.20.Ja Computer simulation of liquid structure
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

High-resolution electron spectroscopy, preferential metal-binding sites, and thermochemistry of lithium complexes of polycyclic aromatic hydrocarbons

Jung Sup Lee, Serge A. Krasnokutski, and Dong-Sheng Yang

J. Chem. Phys. 134, 024301 (2011); http://dx.doi.org/10.1063/1.3523346 (9 pages) | Cited 1 time

Online Publication Date: 11 January 2011

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Polycyclic aromatic hydrocarbons are model systems for studying the mechanisms of lithium storage in carbonaceous materials. In this work, Li complexes of naphthalene, pyrene, perylene, and coronene were synthesized in a supersonic metal-cluster beam source and studied by zero-electron-kinetic-energy (ZEKE) electron spectroscopy and density functional theory calculations. The adiabatic ionization energies of the neutral complexes and frequencies of up to nine vibrational modes in the singly charged cations were determined from the ZEKE spectra. The metal-ligand bond energies of the neutral complexes were obtained from a thermodynamic cycle. Preferred Li/Li+ binding sites with the aromatic molecules were determined by comparing the measured spectra with theoretical calculations. Li and Li+ prefer the ring-over binding to the benzene ring with a higher π-electron content and aromaticity. Although the ionization energies of the Li complexes show no clear correlation with the size of the aromatic molecules, the metal-ligand bond energies increase with the extension of the π-electron network up to perylene, then decrease from perylene to coronene. The trends in the ionization and metal-ligand bond dissociation energies of the complexes are discussed in terms of the orbital energies, local quadrupole moments, and polarizabilities of the free ligands and the charge transfer between the metal atom and aromatic molecules.
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61.25.he Polymer solutions
82.60.Lf Thermodynamics of solutions
34.50.Gb Electronic excitation and ionization of molecules
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
33.15.Fm Bond strengths, dissociation energies
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility

Addition of one and two units of C2H to styrene: A theoretical study of the C10H9 and C12H9 systems and implications toward growth of polycyclic aromatic hydrocarbons at low temperatures

Alexander Landera, Ralf I. Kaiser, and Alexander M. Mebel

J. Chem. Phys. 134, 024302 (2011); http://dx.doi.org/10.1063/1.3526957 (13 pages)

Online Publication Date: 11 January 2011

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Various mechanisms of the formation of naphthalene and its substituted derivatives have been investigated by ab initio G3(MP2,CC)/B3LYP/6-311G** calculations of potential energy surfaces for the reactions of one and two C2H additions to styrene combined with RRKM calculations of product branching ratios under single-collision conditions. The results show that for the C2H + styrene reaction, the dominant routes are H atom eliminations from the initial adducts; C2H addition to the vinyl side chain of styrene is predicted to produce trans or cis conformations of phenylvinylacetylene (t- and c-PVA), whereas C2H addition to the ortho carbon in the ring is expected to lead to the formation of o-ethynylstyrene. Although various reaction channels may lead to a second ring closure and the formation of naphthalene, they are not competitive with the direct H loss channels producing PVAs and ethynylstyrenes. However, c-PVA and o-ethynylstyrene may undergo a second addition of the ethynyl radical to ultimately produce substituted naphthalene derivatives. α- and β-additions of C2H to the side chain in c-PVA are calculated to form 2-ethynyl-naphthalene with branching ratios of about 30% and 96%, respectively; the major product in the case of α-addition would be cis-1-hexene-3,5-diynyl-benzene produced by an immediate H elimination from the initial adduct. C2H addition to the ethynyl side chain in o-ethynylstyrene is predicted to lead to the formation of 1-ethynyl-naphthalene as the dominant product. The C2H + styrene → t-PVA + H/c-PVA + H/ o-ethynylstyrene, C2H + c-PVA → 2-ethynyl-naphthalene + H, and C2H + o-ethynylstyrene → 1-ethynyl-naphthalene + H reactions are calculated to occur without a barrier and with high exothermicity, with all intermediates, transition states, and products lying significantly lower in energy than the initial reactants, and hence to be fast even at very low temperature conditions prevailing in Titan's atmosphere or in the interstellar medium. If styrene and C2H are available and overlap, the sequence of two C2H additions can result in the closure of a second aromatic ring and thus provide a viable route to the formation of 1- or 2-ethynyl-naphthalene. The analogous mechanism can be extrapolated to the low-temperature growth of polycyclic aromatic hydrocarbons (PAH) in general, as a step from a vinyl-PAH to an ethynyl-substituted PAH with an extra aromatic ring.
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82.20.Hf Product distribution
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
82.30.Nr Association, addition, insertion, cluster formation
33.15.Bh General molecular conformation and symmetry; stereochemistry
31.15.A- Ab initio calculations
31.15.E- Density-functional theory

Ultrafast charge separation driven by differential particle and hole mobilities

Anthony D. Dutoi, Michael Wormit, and Lorenz S. Cederbaum

J. Chem. Phys. 134, 024303 (2011); http://dx.doi.org/10.1063/1.3506617 (9 pages)

Online Publication Date: 11 January 2011

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The process of a local excitation evolving into an intramolecular charge-separated state is followed and compared for several systems by directly simulating the time propagation of the electronic wavefunction. The wavefunction and Hamiltonian are handled using the extended second-order algebraic diagrammatic construction (ADC(2)-x), which explicitly accounts for electron correlation in the dynamic many-particle state. The details of the charge separation can be manipulated according to the chemical composition of the system; atoms which dope the conjugated system with either particles or holes are shown to effect whether the particle or hole is more mobile. Initially, the charges oscillate between the ends of linear molecules (with different rates), separating periodically, but, at long times, both charges tend to spread over the whole molecule. Charge separation is also shown to occur for asymmetric systems, where it may eventually be experimentally feasible to excite a localized resonance (nonstationary state) on one end of the molecule preferentially and follow the ensuing dynamics.
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31.15.vq Electron correlation calculations for polyatomic molecules

Role of higher excited electronic states on high harmonic generation in H2+ − a time-independent Hermitian Floquet approach

Chitrakshya Sarkar, S. S. Bhattacharyya, and Samir Saha

J. Chem. Phys. 134, 024304 (2011); http://dx.doi.org/10.1063/1.3524343 (6 pages)

Online Publication Date: 11 January 2011

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We have theoretically studied the role of high-lying molecular electronic states on the high harmonic generation (HHG) in H2+ within the framework of a time-independent Hermitian nonperturbative three-dimensional Floquet technique for continuous wave monochromatic lasers of intensities of 2.59 × 1013, 4.0 × 1013, and 5.6 × 1013 W/cm2, and wavelengths of 1064, 532, and 355 nm. To evaluate the HHG spectra, the resonance Floquet quasienergy and the Fourier components of the Floquet state corresponding to the initial vibrational-rotational level v = 0, J = 0 have been computed by solving the time-independent close-coupled Schrödinger equation following the Floquet method. The calculations include seven molecular electronic states in the basis set expansion of the Floquet state. The electronic states considered, apart from the two lowest 1sσg and 2pσu states, are 2pπu, 2sσg, 3pσu, 3dσg, and 4fσu. All the concerned higher excited molecular electronic states asymptotically degenerate into the atomic state H(2 l) with l = 0, 1. The computations reveal signature of significant oscillations in the HHG spectra due to the interference effect of the higher molecular electronic states for all the considered laser intensities and wavelengths. We have attempted to explain, without invoking any ionization, the dynamics of HHG in H2+ within the framework of electronic transitions due to the electric dipole moments and the nuclear motions on the field coupled ground, the first and the higher excited electronic states of this one-electron molecular ion.
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33.80.Be Level crossing and optical pumping
33.20.Vq Vibration-rotation analysis
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
33.15.Mt Rotation, vibration, and vibration-rotation constants

Calculations of fine-structure resolved collisional rate coefficients for the NH(X3Σ−)-He system

Robert Toboła, Fabien Dumouchel, Jacek Kłos, and François Lique

J. Chem. Phys. 134, 024305 (2011); http://dx.doi.org/10.1063/1.3524311 (8 pages)

Online Publication Date: 11 January 2011

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We present fine-structure-resolved collisional rate coefficients for the NH(X3Σ−)-He van der Waals complex. The calculations are based on the state-of-the-art potential energy surface [Cybulski et al., J. Chem. Phys. 122, 094307 (2005)]. Close-coupling calculations of the collisional excitation cross sections of the fine-structure levels of NH by He are calculated for total energies up to 3500 cm−1, which yield, after thermal average, rate coefficients up to 350 K. The fine-structure splitting of rotational levels is taken into account rigorously. The propensity rules between fine-structure levels are reported, and it is found that F-conserving cross sections are much larger than F-changing cross sections, as expected from theoretical considerations. The calculated rate coefficients are compared with available experimental measurements at room temperature and a fairly good agreement is found between experimental and theoretical data. The agreement confirms the relatively good quality of the scattering calculations and also the accuracy of the potential energy surface used in this work. The new set of thermal rate coefficients for this system may be used for improvements in astrophysical and atmospherical modeling.
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33.15.Pw Fine and hyperfine structure
34.20.Gj Intermolecular and atom-molecule potentials and forces
34.50.-s Scattering of atoms and molecules
31.15.bw Coupled-cluster theory
33.20.Sn Rotational analysis
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