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28 Oct 2008

Volume 129, Issue 16, Articles (16xxxx)

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Exact computation and large angular momentum asymptotics of 3nj symbols: Semiclassical disentangling of spin networks

Roger W. Anderson, Vincenzo Aquilanti, and Cristiane da Silva Ferreira

J. Chem. Phys. 129, 161101 (2008); http://dx.doi.org/10.1063/1.3000578 (5 pages) | Cited 2 times

Online Publication Date: 23 October 2008

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Spin networks, namely, the 3nj symbols of quantum angular momentum theory and their generalizations to groups other than SU(2) and to quantum groups, permeate many areas of pure and applied science. The issues of their computation and characterization for large values of their entries are a challenge for diverse fields, such as spectroscopy and quantum chemistry, molecular and condensed matter physics, quantum computing, and the geometry of space time. Here we record progress both in their efficient calculation and in the study of the large j asymptotics. For the 9j symbol, a prototypical entangled network, we present and extensively check numerically formulas that illustrate the passage to the semiclassical limit, manifesting both the occurrence of disentangling and the discrete-continuum transition.
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03.65.Ta Foundations of quantum mechanics; measurement theory
03.65.Ud Entanglement and quantum nonlocality (e.g. EPR paradox, Bell's inequalities, GHZ states, etc.)
03.65.Sq Semiclassical theories and applications
03.65.Fd Algebraic methods

Iterative Monte Carlo for quantum dynamics

Vikram Jadhao and Nancy Makri

J. Chem. Phys. 129, 161102 (2008); http://dx.doi.org/10.1063/1.3000393 (4 pages) | Cited 10 times

Online Publication Date: 30 October 2008

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We present a fully quantum mechanical methodology for calculating complex-time correlation functions by evaluating the discretized path integral expression iteratively on a grid selected by a Monte Carlo procedure. Both the grid points and the summations performed in each iteration utilize importance sampling, leading to favorable scaling with the number of particles, while the stepwise evaluation of the integrals circumvents the exponential growth of statistical error with time.
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03.67.Ac Quantum algorithms, protocols, and simulations
02.70.Ss Quantum Monte Carlo methods
05.10.Ln Monte Carlo methods

Attosecond nonlinear Fourier transformation spectroscopy of CO2 in extreme ultraviolet wavelength region

Tomoya Okino, Kaoru Yamanouchi, Toshihiko Shimizu, Ri Ma, Yasuo Nabekawa, and Katsumi Midorikawa

J. Chem. Phys. 129, 161103 (2008); http://dx.doi.org/10.1063/1.3006026 (4 pages) | Cited 7 times

Online Publication Date: 31 October 2008

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The interferometric autocorrelation functions of attosecond pulse trains in the time domain were measured by detecting CO22+ as well as the atomic and molecular fragment ions generated via two-photon absorption of intense vacuum ultraviolet-extreme ultraviolet light by CO2. It was demonstrated that the Fourier transformation of the interferometric autocorrelation functions of the respective fragment ions appearing in a time-of-flight mass spectrum exhibit spectroscopic information in the frequency domain corresponding to the two-photon photofragment excitation spectra of CO2 and the double ionization excitation spectrum to form CO22+.
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33.20.Lg Ultraviolet spectra
32.30.Jc Visible and ultraviolet spectra
32.80.Fb Photoionization of atoms and ions
32.80.Rm Multiphoton ionization and excitation to highly excited states
33.80.Eh Autoionization, photoionization, and photodetachment
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
42.65.-k Nonlinear optics
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Enthalpy difference between conformations of normal alkanes: Intramolecular basis set superposition error (BSSE) in the case of n-butane and n-hexane

Roman M. Balabin

J. Chem. Phys. 129, 164101 (2008); http://dx.doi.org/10.1063/1.2997349 (5 pages) | Cited 27 times

Online Publication Date: 22 October 2008

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In this paper, an extra error source for high-quality ab initio calculation of conformation equilibrium in normal alkanes—intramolecular basis set superposition error (BSSE)—is discussed. Normal butane (n-butane) and normal hexane (n-hexane) are used as representative examples. Single-point energy difference and BSSE values of trans and gauche conformations for n-butane (and trans-trans-trans and gauche-gauche-gauche conformations for n-hexane) were calculated using popular electron correlation methods: The second-order Moller–Plesset (MP2), the fourth-order Moller–Plesset (MP4), and coupled cluster with single and double substitutions with noniterative triple excitation [CCSD(T)] levels of theory. Extrapolation to the complete basis set is applied. The difference between BSSE-corrected and uncorrected relative energy values ranges from ∼ 100 cal/mol (in case of n-butane) to more than 1000 cal/mol (in case of n-hexane). The influence of basis set type (Pople or Dunning) and size [up to 6-311G(3df,3pd) and aug-cc-pVQZ] is discussed.
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31.15.am Relativistic configuration interaction (CI) and many-body perturbation calculations
31.15.V- Electron correlation calculations for atoms, ions and molecules
31.15.xp Perturbation theory
31.15.bw Coupled-cluster theory
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)

Excitation mechanism in the photoisomerization of a surface-bound azobenzene derivative: Role of the metallic substrate

Sebastian Hagen, Peter Kate, Felix Leyssner, Dhananjay Nandi, Martin Wolf, and Petra Tegeder

J. Chem. Phys. 129, 164102 (2008); http://dx.doi.org/10.1063/1.2997343 (8 pages) | Cited 21 times

Online Publication Date: 22 October 2008

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Two-photon photoemission spectroscopy is employed to elucidate the electronic structure and the excitation mechanism in the photoinduced isomerization of the molecular switch tetra-tert-butyl-azobenzene (TBA) adsorbed on Au(111). Our results demonstrate that the optical excitation and the mechanism of molecular switching at a metal surface is completely different compared to the corresponding process for the free molecule. In contrast to direct (intramolecular) excitation operative in the isomerization in the liquid phase, the conformational change in the surface-bound TBA is driven by a substrate-mediated charge transfer process. We find that photoexcitation above a threshold hν ≈ 2.2 eV leads to hole formation in the Au d-band followed by a hole transfer to the highest occupied molecular orbital of TBA. This transiently formed positive ion resonance subsequently results in a conformational change. The photon energy dependent photoisomerization cross section exhibit an unusual shape for a photochemical reaction of an adsorbate on a metal surface. It shows a thresholdlike behavior below hν ≈ 2.2 eV and above hν ≈ 4.4 eV. These thresholds correspond to the minimum energy required to create single or multiple hot holes in the Au d-bands, respectively. This study provides important new insights into the use of light to control the structure and function of molecular switches in direct contact with metal electrodes.
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82.30.Qt Isomerization and rearrangement
82.50.Pt Multiphoton processes
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions

Improving the B3LYP bond energies by using the X1 method

Jianming Wu and Xin Xu

J. Chem. Phys. 129, 164103 (2008); http://dx.doi.org/10.1063/1.2998231 (11 pages) | Cited 11 times

Online Publication Date: 22 October 2008

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Recently, we proposed the X1 method which combines density functional theory method (B3LYP) with a neural network correction for an accurate yet efficient prediction of heats of formation [ J. M. Wu and X. Xu, J. Chem. Phys. 127, 214105 (2007) ]. In the present work, we examine the X1 performance to calculate bond energies. We use 32 radicals and 115 molecules to set up 142 bond dissociation reactions. For the total of 147 heats of formations and 142 bond energies, B3LYP leads to mean absolute deviations of 4.54 and 6.26 kcal/mol, respectively, while X1 reduces the corresponding errors to 1.41 and 2.45 kcal/mol.
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82.20.-w Chemical kinetics and dynamics
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.60.Cx Enthalpies of combustion, reaction, and formation

A comparative investigation of H2 adsorption strength in Cd- and Zn-based metal organic framework-5

Pornjuk Srepusharawoot, C. Moysés Araújo, Andreas Blomqvist, Ralph H. Scheicher, and Rajeev Ahuja

J. Chem. Phys. 129, 164104 (2008); http://dx.doi.org/10.1063/1.2997377 (5 pages) | Cited 5 times

Online Publication Date: 22 October 2008

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Hydrogen binding energies for the primary and secondary adsorption sites in the Cd- and Zn-based metal organic framework-5 (MOF-5) were studied using density functional theory. Out of the three exchange-correlation functionals employed in our study, we find that the local density approximation yields a qualitatively correct description of the interaction strengths of H2 in MOF-5 systems. The H2 adsorption energies for all trapping sites in Zn- and Cd-based MOF-5 are seen to be of the same order of magnitude but with a generally stronger binding in Cd-based MOF-5 as compared to Zn-based MOF-5. In particular, the H2 binding energy at the secondary adsorption sites in Cd-based MOF-5 is increased by around 25% compared to Zn-based MOF-5. This result suggests that Cd-based MOF-5 would be better suited to store hydrogen at higher temperatures than Zn-based MOF-5.
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84.60.-h Direct energy conversion and storage
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

A density matrix functional with occupation number driven treatment of dynamical and nondynamical correlation

Daniel R. Rohr, Katarzyna Pernal, Oleg V. Gritsenko, and Evert Jan Baerends

J. Chem. Phys. 129, 164105 (2008); http://dx.doi.org/10.1063/1.2998201 (11 pages) | Cited 28 times

Online Publication Date: 23 October 2008

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A recently proposed series of corrections to the earliest JK-only functionals has considerably improved the prospects of density matrix functional theory (DMFT). Still, the most advanced of these functionals (correction C3) requires a preselection of the terms in the pair density Γ(r1,r2) involving the bonding and antibonding natural orbitals (NOs) belonging to an electron pair bond. Ideally, a DMFT functional should only depend on the NOs and their occupation numbers, and we propose a functional with an occupation number driven weighing of terms in the pair density. These are formulated as “damping” for certain ranges of occupation numbers of the two-electron cumulant that arises in the expansion of the two-particle density matrix of the paradigmatic two-electron system. This automatic version of C3, which we denote AC3, provides the correct dissociation limit for electron pair bonds and it excellently reproduces the potential energy curves of the multireference configuration interaction (MRCI) method for the dissociation of the electron pair bond in the series of the ten-electron hydrides CH4, NH3, H2O, and HF. AC3 reproduces closely the experimental equilibrium distances and at Re it yields correlation energies of the ten-electron systems with an average error in the absolute values of only 3.3% compared to the MRCI values. We stress the importance of treatment of strong correlation cases (NO occupation numbers differing significantly from 2.0 and 0.0) by appropriate terms in the cumulant.
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31.15.eg Exchange-correlation functionals (in current density functional theory)
31.15.vn Electron correlation calculations for diatomic molecules
31.50.-x Potential energy surfaces
33.15.Bh General molecular conformation and symmetry; stereochemistry

A local contracted treatment of single and double excitations

P. Reinhardt, H. Zhang, J. Ma, and J.-P. Malrieu

J. Chem. Phys. 129, 164106 (2008); http://dx.doi.org/10.1063/1.2996126 (9 pages) | Cited 4 times

Online Publication Date: 24 October 2008

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Starting from localized bond or lone-pair Hartree–Fock molecular orbitals, one may define contracted doubly excited functions for each pair of bond molecular orbitals. These functions are obtained from local single- and double-configuration interaction (CISD) of moderate size. Then one may build a contracted CISD matrix for the whole molecule, spanned by the Hartree–Fock determinant and these contracted doubly excited functions, the number of which is indeed moderate, as scaling at most as the square of the number of bonds. The calculation of the off-diagonal elements of this matrix is straightforward. Its diagonalization provides an upper bound to the lowest CISD eigenvalue. The well-known size-consistency error may be overcome through self-consistent dressings such as coupled-electron pair approximations, and cutoff criteria will lead to linear scaling. Numerical tests on a series of covalent and ionic systems show that the results are very close to that of coupled-cluster calculations. Possible improvements of this already efficient algorithm are suggested.
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31.15.V- Electron correlation calculations for atoms, ions and molecules
31.15.xr Self-consistent-field methods

Predicting accurate vibrational frequencies for highly anharmonic systems

Bosiljka Njegic and Mark S. Gordon

J. Chem. Phys. 129, 164107 (2008); http://dx.doi.org/10.1063/1.2987712 (13 pages) | Cited 9 times

Online Publication Date: 24 October 2008

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Improvements in the manner in which the potential energy surface (PES) is generated in the vibrational self-consistent field (VSCF) method have been implemented. The PES can now be computed over a flexible range of displacements and following normal mode displacement vectors expressed in internal rather than Cartesian coordinates, leading to higher accuracy of the calculated vibrational frequencies. The coarse-grained parallelization of the PES calculations, which is computationally by far the most expensive part of the VSCF method, enables the usage of higher levels of theory and larger basis sets. The new VSCF procedure is discussed and applied to three examples, H3+, HNO2, and HNO3, to illustrate its accuracy and applicability.
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33.20.Tp Vibrational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
31.15.xr Self-consistent-field methods
31.50.-x Potential energy surfaces

Density functional localized orbital corrections for transition metals

David Rinaldo, Li Tian, Jeremy N. Harvey, and Richard A. Friesner

J. Chem. Phys. 129, 164108 (2008); http://dx.doi.org/10.1063/1.2974101 (23 pages)

Online Publication Date: 24 October 2008

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This paper describes the development of the B3LYP localized orbital correction model which improves the accuracy of the B3LYP thermochemical predictions for compounds containing transition metals. The development of this model employs a large data set containing 36 experimental atomic energies and 71 bond dissociation energies. B3LYP calculations were carried out on these systems with different basis sets. Based on an electronic structure analysis and physical arguments, we built a set of 10 parameters to correct atomic data and a set of 21 parameters to correct bond dissociation energies. Using the results from our biggest basis set, the model was shown to reduce the mean absolute deviation from 7.7 to 0.4 kcal/mol for the atomic data and from 5.3 to 1.7 kcal/mol for the bond dissociation energies. The model was also tested using a second basis set and was shown to give relatively accurate results too. The model was also able to predict an outlier in the experimental data that was further investigated with high level coupled-cluster calculations.
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31.15.E- Density-functional theory
31.15.bw Coupled-cluster theory

An analysis of the correlation energy contribution to the interaction energy of inert gas dimers

Ian Snook, Manolo C. Per, and Salvy P. Russo

J. Chem. Phys. 129, 164109 (2008); http://dx.doi.org/10.1063/1.2988150 (5 pages) | Cited 2 times

Online Publication Date: 24 October 2008

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An accurate description of electron correlation is essential for the calculation of interaction energies in cases where dispersion energy is a major component, for example, for the rare gas atoms, physisorption on graphite, and graphene-graphene interactions. Such calculations are computationally demanding using supermolecule methods and the energies calculated lack a simple, physical interpretation. Alternatively density functional theories (DFTs) may be used to give an approximate estimate of the correlation energy. However, the physical nature of this DFT estimate of electron correlation energy is not well understood and, in fact, most current DFT methods do not describe dispersion energy at all. Hence, an analysis of the correlation energy contribution to interaction energies where dispersion energy is important is needed. In order to do this we provide an analysis of the correlation energy contribution to the potential energy curves of He2, Ne2, and Ar2 in terms of the Hartree–Fock (HF) interaction term ΔEintHF, a dispersion energy term Edisp and an electron correlation term ΔEintC. ΔEintC includes all other correlation energy effects besides Edisp and is shown to be repulsive, of a similar short range character to, but of smaller magnitude than ΔEintHF. This analysis was used to develop a theoretical model which gives a very good estimate of the potential energy wells for He2, Ne2, Ar2, HeNe, HeAr, and NeAr.
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34.20.Gj Intermolecular and atom-molecule potentials and forces
31.50.-x Potential energy surfaces
31.15.V- Electron correlation calculations for atoms, ions and molecules
31.15.xr Self-consistent-field methods

Analytical calculations of frequency-dependent hypermagnetizabilities and Cotton–Mouton constants using London atomic orbitals

Andreas J. Thorvaldsen, Kenneth Ruud, Antonio Rizzo, and Sonia Coriani

J. Chem. Phys. 129, 164110 (2008); http://dx.doi.org/10.1063/1.2993325 (14 pages) | Cited 9 times

Online Publication Date: 27 October 2008

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We present the first gauge-origin-independent, frequency-dependent calculations of the hypermagnetizability anisotropy, which determines the temperature-independent contribution to magnetic-field-induced linear birefringence, the so-called Cotton–Mouton effect. A density-matrix-based scheme for analytical calculations of frequency-dependent molecular properties for self-consistent field models has recently been developed, which is also valid with frequency- and field-dependent basis sets. Applying this scheme to Hartree–Fock wave functions and using London atomic orbitals in order to obtain gauge-origin-independent results, we have calculated the hypermagnetizability anisotropy. Our results show that the use of London orbitals leads to somewhat better basis-set convergence for the hypermagnetizability compared to conventional basis sets and that London orbitals are mandatory in order to obtain reliable magnetizability anisotropies.
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78.20.Ls Magneto-optical effects
75.30.Gw Magnetic anisotropy
75.10.-b General theory and models of magnetic ordering

Nonadiabatic simulation study of photoisomerization of azobenzene: Detailed mechanism and load-resisting capacity

Junfeng Shao, Yibo Lei, Zhenyi Wen, Yusheng Dou, and Zhisong Wang

J. Chem. Phys. 129, 164111 (2008); http://dx.doi.org/10.1063/1.3000008 (9 pages) | Cited 8 times

Online Publication Date: 27 October 2008

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Nonadiabatic dynamical simulations were carried out to study cis-to-trans isomerization of azobenzene under laser irradiation and/or external mechanical loads. We used a semiclassical electron-radiation-ion dynamics method that is able to describe the coevolution of the structural dynamics and the underlying electronic dynamics in a real-time manner. It is found that azobenzene photoisomerization occurs predominantly by an out-of-plane rotation mechanism even under a nontrivial resisting force of several tens of piconewtons. We have repeated the simulations systematically for a broad range of parameters for laser pulses, but could not find any photoisomerization event by a previously suggested in-plane inversion mechanism. The simulations found that the photoisomerization process can be held back by an external resisting force of 90–200 pN depending on the frequency and intensity of the lasers. This study also found that a pure mechanical isomerization is possible from the cis-to-trans state if the azobenzene molecule is stretched by an external force of ∼ 1250–1650 pN. Remarkably, the mechanical isomerization first proceeds through a mechanically activated inversion, and then is diverted to an ultrafast downhill rotation that accomplishes the isomerization. Implications of these findings to azobenzene-based nanomechanical devices are discussed.
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82.30.Qt Isomerization and rearrangement
82.50.-m Photochemistry
82.20.Gk Electronically non-adiabatic reactions

Preserving the Boltzmann ensemble in replica-exchange molecular dynamics

Ben Cooke and Scott C. Schmidler

J. Chem. Phys. 129, 164112 (2008); http://dx.doi.org/10.1063/1.2989802 (17 pages) | Cited 8 times

Online Publication Date: 27 October 2008

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We consider the convergence behavior of replica-exchange molecular dynamics (REMD) [ Sugita and Okamoto, Chem. Phys. Lett. 314, 141 (1999) ] based on properties of the numerical integrators in the underlying isothermal molecular dynamics (MD) simulations. We show that a variety of deterministic algorithms favored by molecular dynamics practitioners for constant-temperature simulation of biomolecules fail either to be measure invariant or irreducible, and are therefore not ergodic. We then show that REMD using these algorithms also fails to be ergodic. As a result, the entire configuration space may not be explored even in an infinitely long simulation, and the simulation may not converge to the desired equilibrium Boltzmann ensemble. Moreover, our analysis shows that for initial configurations with unfavorable energy, it may be impossible for the system to reach a region surrounding the minimum energy configuration. We demonstrate these failures of REMD algorithms for three small systems: a Gaussian distribution (simple harmonic oscillator dynamics), a bimodal mixture of Gaussians distribution, and the alanine dipeptide. Examination of the resulting phase plots and equilibrium configuration densities indicates significant errors in the ensemble generated by REMD simulation. We describe a simple modification to address these failures based on a stochastic hybrid Monte Carlo correction, and prove that this is ergodic.
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31.15.xv Molecular dynamics and other numerical methods
02.70.Ns Molecular dynamics and particle methods

Phase diagram of a model of nanoparticles in electrolyte solutions

Xiaofei Li, S. Lettieri, N. Wentzel, and J. D. Gunton

J. Chem. Phys. 129, 164113 (2008); http://dx.doi.org/10.1063/1.2999608 (6 pages) | Cited 2 times

Online Publication Date: 28 October 2008

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We obtain accurate fluid-fluid coexistence curves for a recent simple model of interacting nanoparticles that includes the effects of ion-dispersion forces. It has been proposed that these ion-dispersion forces provide at least a partial explanation for the Hofmeister effect [ M. Boström et al. Phys. Rev. Lett. 87, 168103 (2001) ]. We study a model of aluminum oxide nanoparticle [ Deniz et al., Colloids Surf. A 319, 98 (2008) ] for three different electrolyte solutions with added salt type being sodium chloride, sodium iodide, and a nonpolarizable salt. We observe that the fluid-fluid coexistence curves depend substantially on the identity of added salt; this provides an efficient way of tuning the phase behavior of nanoparticles. The methods we employ include finite-size scaling (FSS), multicanonical histogram reweighting, and Gibbs ensemble methods. We show that, as expected, all three cases belong to the Ising universality class. The scaling fields and critical point parameters are obtained in the thermodynamic limit of infinite system size by extrapolation of our FSS results.
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81.30.Dz Phase diagrams of other materials
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
82.45.Gj Electrolytes
82.45.Yz Nanostructured materials in electrochemistry

Aromaticity in spin-polarized systems: Can rings be simultaneously alpha aromatic and beta antiaromatic?

Marcos Mandado, Ana M. Graña, and Ignacio Pérez-Juste

J. Chem. Phys. 129, 164114 (2008); http://dx.doi.org/10.1063/1.2999562 (7 pages) | Cited 1 time

Online Publication Date: 28 October 2008

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The partition of the multicenter electron delocalization indices and the nucleus independent chemical shift indices into alpha and beta contributions in open-shell systems has been performed. In general it is shown that a full understanding of aromaticity in these systems cannot be achieved by restricting the calculations to the global properties but by dissecting these properties into α and β terms. The 4n+2- and 4n-aromaticity rules for singlet and triplet annulenes, respectively, reduce to a general aromaticity rule when the α and β terms are studied separately. This new rule allows us to extend the concept of conflicting aromaticities to radical systems that are simultaneously α-aromatic and β-antiaromatic or vice versa. The existence of such systems is demonstrated here by means of multicenter electron delocalization indices and nucleus independent chemical shifts. Finally, the global aromatic/antiaromatic character of these radical systems is estimated by means of aromatic stabilization energy, which is shown to be either slightly positive or slightly negative, thus reflecting the small aromatic/antiaromatic character of these radicals and reinforcing the conclusions obtained with aromaticity indices.
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36.20.Hb Configuration (bonds, dimensions)
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
76.60.Cq Chemical and Knight shifts

Energy-consistent small-core pseudopotentials for 3d-transition metals adapted to quantum Monte Carlo calculations

M. Burkatzki, Claudia Filippi, and M. Dolg

J. Chem. Phys. 129, 164115 (2008); http://dx.doi.org/10.1063/1.2987872 (7 pages) | Cited 8 times

Online Publication Date: 29 October 2008

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We extend our recently published set of energy-consistent scalar-relativistic Hartree–Fock pseudopotentials by the 3d-transition metal elements, scandium through zinc. The pseudopotentials do not exhibit a singularity at the nucleus and are therefore suitable for quantum Monte Carlo (QMC) calculations. The pseudopotentials and the accompanying basis sets (VnZ with n = T,Q) are given in standard Gaussian representation and their parameter sets are presented. Coupled cluster, configuration interaction, and QMC studies are carried out for the scandium and titanium atoms and their oxides, demonstrating the good performance of the pseudopotentials. Even though the choice of pseudopotential form is motivated by QMC, these pseudopotentials can also be employed in other quantum chemical approaches.
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31.15.am Relativistic configuration interaction (CI) and many-body perturbation calculations
31.15.xr Self-consistent-field methods
31.15.bw Coupled-cluster theory

An explicit algorithm for fully flexible unit cell simulation with recursive thermostat chains

Kwangsub Jung and Maenghyo Cho

J. Chem. Phys. 129, 164116 (2008); http://dx.doi.org/10.1063/1.2998307 (11 pages) | Cited 1 time

Online Publication Date: 29 October 2008

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Through the combination of the recursive multiple thermostat (RMT) Nosé–Poincaré and Parrinello–Rahman methods, the recursive multiple thermostat chained fully flexible unit cell (RMT-NσT) molecular dynamics method is proposed for isothermal-isobaric simulation. The RMT method is known to have the advantage of achieving the ergodicity that is required for canonical sampling of the harmonic oscillator. Thus, an explicit time integration algorithm is developed for RMT-NσT. We examine the ergodicity for various parameters of RMT-NσT using bulk and thin film structures with different numbers of copper atoms and thicknesses in various environments. Through the numerical simulations, we conclude that the RMT-NσT method is advantageous in the cases of lower temperatures.
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68.55.-a Thin film structure and morphology
68.60.Bs Mechanical and acoustical properties

Band gap change and interfacial reaction in Hf-silicate film grown on Ge(001)

Y.-J. Cho, W. J. Lee, C. Y. Kim, M.-H. Cho, H. Kim, H. J. Lee, D. W. Moon, and H. J. Kang

J. Chem. Phys. 129, 164117 (2008); http://dx.doi.org/10.1063/1.3000392 (4 pages) | Cited 2 times

Online Publication Date: 29 October 2008

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The interfacial reaction of hafnium-silicate [(HfO2)x(SiO2)1−x, x = 0.5,0.7] thin films grown on Ge(001) by atomic layer deposition was investigated using x-ray photoelectron spectroscopy and medium energy ion scattering spectroscopy. According to the peak changes in Hf 4f and Ge 3d, the Hf-silicate film reacted with the oxidized Ge surface forming Hf-germanate at the interface. The formation of Hf-germanate induced band bending of the Ge substrate at the interface and decreased band gap to 5.1 eV, which was lower than that of GeO2 (5.6 eV). In particular, the interfacial reaction was dependent on the amount of SiO2 in the Hf-silicate film, which resulted in more decrement in the band gap in the film with a high SiO2 fraction.
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71.20.Ps Other inorganic compounds
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
79.60.Dp Adsorbed layers and thin films
68.55.aj Insulators

Nonadiabatic dynamics and simulation of time resolved photoelectron spectra within time-dependent density functional theory: Ultrafast photoswitching in benzylideneaniline

Roland Mitrić, Ute Werner, and Vlasta Bonačić-Koutecký

J. Chem. Phys. 129, 164118 (2008); http://dx.doi.org/10.1063/1.3000012 (9 pages) | Cited 12 times

Online Publication Date: 29 October 2008

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We present a theoretical approach for the nonadiabatic dynamics “on the fly” based on the combination of the time-dependent density functional theory (TDDFT) with Tully’s stochastic surface hopping method. Our formulation is based on localized Gaussian basis sets and is suitable for the simulation of ultrafast processes in complex molecular systems including all degrees of freedom. Our approach is used for the simulation of time resolved photoelectron spectra in the framework of the Wigner distribution approach. In order to illustrate the scope of the method, we study the ultrafast photoswitching dynamics of the prototype Schiff base benzylideneaniline (BAN). The nonradiative lifetime of the S1 state of BAN is determined to be ∼ 200 fs. The mechanism of the photoisomerization has been investigated and a connection between the time resolved photoelectron signal and the underlying nonadiabatic processes has been established.
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82.50.-m Photochemistry
82.53.Kp Coherent spectroscopy of atoms and molecules
82.30.Qt Isomerization and rearrangement
82.20.Gk Electronically non-adiabatic reactions
82.20.Db Transition state theory and statistical theories of rate constants
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Relativistic corrections to electrical first-order properties using direct perturbation theory

Stella Stopkowicz and Jürgen Gauss

J. Chem. Phys. 129, 164119 (2008); http://dx.doi.org/10.1063/1.2998300 (9 pages) | Cited 13 times

Online Publication Date: 31 October 2008

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Direct perturbation theory (DPT) is applied to compute relativistic corrections to electrical properties such as dipole moment, quadrupole moment, and electric-field gradient. The corrections are obtained as second derivatives of the energy and are given via method-independent expressions that involve the first derivative of the density matrix with respect to the relativistic perturbation as well as property integrals with additional momentum operators. Computational results obtained using Hartree–Fock (HF), second-order Møller–Plesset (MP2) perturbation theory, and the coupled-cluster singles and doubles approach augmented by a perturbative treatment of triple excitations are presented for the hydrogen halides HX with X = F, Cl, Br, (I, At) and the magnitude of relativistic effects, their basis-set dependence, and the limitations of DPT are discussed. We compare our results to those obtained using the second-order Douglas–Kroll method and benchmark them using four-component HF (Dirac–HF) and MP2 calculations. Relativistic effects are shown to be already important for elements of the third row (Na–Ar) when aiming at a high-accuracy quantum-chemical treatment. DPT provides reliable results for compounds containing elements up to the fourth period (K–Kr) and only breaks down when applied in lowest order to heavier elements. As a first application of the present DPT treatment for electrical properties, we report calculations for bromofluoromethane (CH2FBr) which was investigated using rotational spectroscopy by Cazzoli et al. [ Mol. Phys. 106, 1181 (2008) ] and for which consideration of relativistic effects turns out to be essential for good agreement between theory and experiment in the case of the bromine quadrupole-coupling constant.
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31.30.J- Relativistic and quantum electrodynamic (QED) effects in atoms, molecules, and ions
31.15.xp Perturbation theory
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
31.30.jp Electron electric dipole moment
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

Sub-Doppler spectroscopy of the math 2Σ+−math 2Π and math 2Π−math 2Π transitions of NCO

Nicola L. Elliott, James A. J. Fitzpatrick, and Colin M. Western

J. Chem. Phys. 129, 164301 (2008); http://dx.doi.org/10.1063/1.2987305 (13 pages) | Cited 1 time

Online Publication Date: 22 October 2008

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Sub-Doppler laser induced florescence spectra were recorded of a selection of bands within the math 2Σ+−math 2Π and math 2Π−math 2Π transitions of NCO in a supersonic molecular beam. The light source was a diode seeded optical parametric oscillator, which gave an effective resolution of 0.01 cm−1 in the ultraviolet. Analysis of the math 2Σ+−math 2Π transition at high resolution allowed fitting of both the fine and hyperfine structures, and a set of rotational and hyperfine constants were obtained for 13 vibronic levels within the math 2Σ+ state including levels of both 2Σ+ and 2Π vibronic characters. Analysis of the 000 and 101 bands of the math 2Π−math 2Π transition, together with a band from the math 2Σ+ state at the same energy, was also performed. These did not reveal any hyperfine structure although the resolution was the same as the work at lower total energy, and this observation is discussed. Refined rotational constants and perturbation parameters for the interaction between the math and math states were also obtained.
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33.50.Dq Fluorescence and phosphorescence spectra
33.20.Sn Rotational analysis
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
33.80.-b Photon interactions with molecules
33.15.Pw Fine and hyperfine structure
33.15.Mt Rotation, vibration, and vibration-rotation constants

A quantum chemical study of H2S2: Intramolecular torsional mode and intermolecular interactions with rare gases

Glauciete S. Maciel, Patricia R. P. Barreto, Federico Palazzetti, Andrea Lombardi, and Vincenzo Aquilanti

J. Chem. Phys. 129, 164302 (2008); http://dx.doi.org/10.1063/1.2994732 (10 pages) | Cited 11 times

Online Publication Date: 23 October 2008

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The structural and energetic properties of the H2S2 molecule have been studied using density functional theory, second-order Møller–Plesset method, and coupled cluster theory with several basis sets. In order to extend previous work on intra- and intermolecular dynamics of the chirality changing modes for H2O2 and its derivatives, our focus has been on the torsion around the S–S bond, along with an extensive characterization of the intermolecular potentials of H2S2 with the rare gases (He, Ne, Ar, and Kr). Use is made of previously defined coordinates and expansion formulas for the potentials which allow for a faithful representation of geometrical and symmetry properties of these systems that involve the interaction of an atom with a floppy molecule. The potential energy surfaces obtained in this work are useful for classical and quantum mechanical simulations of molecular collisions responsible for chirality changing processes of possible interest in the modeling of prebiotic phenomena.
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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.Bh General molecular conformation and symmetry; stereochemistry
31.15.bw Coupled-cluster theory
31.50.-x Potential energy surfaces
31.15.xp Perturbation theory

Nonadiabatic orientation, toroidal current, and induced magnetic field in BeO molecules

Ingo Barth, Luis Serrano-Andrés, and Tamar Seideman

J. Chem. Phys. 129, 164303 (2008); http://dx.doi.org/10.1063/1.2994737 (12 pages) | Cited 8 times

Online Publication Date: 23 October 2008

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It is predicted that oriented BeO molecules would give rise to unprecedentedly strong, unidirectional electric ring current and an associated magnetic field upon excitation by a right or left circularly polarized laser pulse into the first excited degenerate singlet state. The strong toroidal electric ring current of this state is dominated by the ring current of the 1π± orbital about the molecular axis. Our predictions are based on the analysis of the orbital composition of the states involved and are substantiated by high level electronic structure calculations and wavepacket simulations of the laser-driven orientation and excitation dynamics.
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33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
33.90.+h Other topics in molecular properties and interactions with photons (restricted to new topics in section 33)
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
31.15.am Relativistic configuration interaction (CI) and many-body perturbation calculations
31.15.bw Coupled-cluster theory
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