JCP Nameplate
  • Volume/Page
  • Keyword
  • DOI
  • Citation
  • Advanced
   
 
 
 

You Tube Flickr Twitter UniPHY Group iResearch App Facebook

BROWSE VOLUMES

Year Range: 
Search Issue | RSS Feeds RSS
Previous Issue Next Issue

28 Jul 2009

Volume 131, Issue 4, Articles (04xxxx)

Issue Cover Spotlight Figure

J. Chem. Phys. 131, 044105 (2009); http://dx.doi.org/10.1063/1.3168400 (8 pages)

Joana G. Freire, Richard J. Field, and Jason A. C. Gallas
Enlarge Image | Read More
Page 1 of 5 Pages Next Page | Jump to Page
back to top
RSS Feeds
FREE

Announcement: The Journal of Chemical Physics eliminates color-printing fees effective 1 August 2009

Mark M. Cassar

J. Chem. Phys. 131, 040201 (2009); http://dx.doi.org/10.1063/1.3198228 (1 page)

Online Publication Date: 31 July 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Show PACS
01.10.Cr Announcements, news, and awards
back to top
RSS Feeds
FREE

Efficient evaluation of accuracy of molecular quantum dynamics using dephasing representation

Baiqing Li, Cesare Mollica, and Jiří Vaníček

J. Chem. Phys. 131, 041101 (2009); http://dx.doi.org/10.1063/1.3187240 (4 pages) | Cited 6 times

Online Publication Date: 23 July 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Ab initio methods for the electronic structure of molecules have reached a satisfactory accuracy for calculations of static properties but remain too expensive for quantum dynamics calculations. We propose an efficient semiclassical method for evaluating the accuracy of a lower level quantum dynamics, as compared to a higher level quantum dynamics, without having to perform any quantum dynamics. The method is based on the dephasing representation of quantum fidelity and its feasibility is demonstrated on the photodissociation dynamics of CO2. Our accuracy test can be easily implemented in existing molecular dynamics codes, thus offering wide applicability.
Show PACS
33.80.Gj Diffuse spectra; predissociation, photodissociation
31.15.ae Electronic structure and bonding characteristics
back to top
RSS Feeds
back to top Theoretical Methods and Algorithms

Nonmetallic electronegativity equalization and point-dipole interaction model including exchange interactions for molecular dipole moments and polarizabilities

Hans S. Smalø, Per-Olof Åstrand, and Lasse Jensen

J. Chem. Phys. 131, 044101 (2009); http://dx.doi.org/10.1063/1.3166142 (19 pages) | Cited 5 times

Online Publication Date: 22 July 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The electronegativity equalization model (EEM) has been combined with a point-dipole interaction model to obtain a molecular mechanics model consisting of atomic charges, atomic dipole moments, and two-atom relay tensors to describe molecular dipole moments and molecular dipole-dipole polarizabilities. The EEM has been phrased as an atom-atom charge-transfer model allowing for a modification of the charge-transfer terms to avoid that the polarizability approaches infinity for two particles at infinite distance and for long chains. In the present work, these shortcomings have been resolved by adding an energy term for transporting charges through individual atoms. A Gaussian distribution is adopted for the atomic charge distributions, resulting in a damping of the electrostatic interactions at short distances. Assuming that an interatomic exchange term may be described as the overlap between two electronic charge distributions, the EEM has also been extended by a short-range exchange term. The result is a molecular mechanics model where the difference of charge transfer in insulating and metallic systems is modeled regarding the difference in bond length between different types of system. For example, the model is capable of modeling charge transfer in both alkanes and alkenes with alternating double bonds with the same set of carbon parameters only relying on the difference in bond length between carbon σ- and π-bonds. Analytical results have been obtained for the polarizability of a long linear chain. These results show that the model is capable of describing the polarizability scaling both linearly and nonlinearly with the size of the system. Similarly, a linear chain with an end atom with a high electronegativity has been analyzed analytically. The dipole moment of this model system can either be independent of the length or increase linearly with the length of the chain. In addition, the model has been parametrized for alkane and alkene chains with data from density functional theory calculations, where the polarizability behaves differently with the chain length. For the molecular dipole moment, the same two systems have been studied with an aldehyde end group. Both the molecular polarizability and the dipole moment are well described as a function of the chain length for both alkane and alkene chains demonstrating the power of the presented model.
Show PACS
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
61.50.Lt Crystal binding; cohesive energy

Gas content of binary clathrate hydrates with promoters

N. I. Papadimitriou, I. N. Tsimpanogiannis, and A. K. Stubos

J. Chem. Phys. 131, 044102 (2009); http://dx.doi.org/10.1063/1.3160767 (10 pages) | Cited 1 time

Online Publication Date: 22 July 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We develop a methodology to calculate the gas storage capacity of binary hydrates stabilized by promoters. This model utilizes equilibrium experimental data of both hydrates (i.e., the hydrate of pure promoter and the binary hydrate of gas and promoter) in order to calculate the gas occupancy in the small cavities that are not occupied by the promoter. The new approach, although based on the traditional van der Waals–Platteeuw theory, has two significant advantages. The hypothetical state of an empty hydrate for the calculation of the chemical potential of water is replaced by the hydrate of the pure promoter whose properties can be determined through simple thermodynamic calculations. In addition, the computational difficulties related to the complete occupancy of the large cavities by the promoter are removed. The proposed methodology is applied to calculate the gas storage capacity of hydrates of two energy-carrier gases (methane and hydrogen) stabilized by tetrahydrofuran. Excellent agreement is observed between the proposed-model predictions and published experimental values for the gas content of hydrates.
Show PACS
34.20.Gj Intermolecular and atom-molecule potentials and forces
82.60.Hc Chemical equilibria and equilibrium constants

On the Kohn–Sham density response in a localized basis set

Dietrich Foerster and Peter Koval

J. Chem. Phys. 131, 044103 (2009); http://dx.doi.org/10.1063/1.3179755 (9 pages) | Cited 4 times

Online Publication Date: 22 July 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We construct the Kohn–Sham density response function χ0 in a previously described basis of the space of orbital products. The calculational complexity of our construction is O(N2Nω) for a molecule of N atoms and in a spectroscopic window of Nω frequency points. As a first application, we use χ0 to calculate the molecular spectra from the Petersilka–Gossmann–Gross equation. With χ0 as input, we obtain the correct spectra with an extra computational effort that grows also as O(N2Nω) and, therefore, less steeply in N than the O(N3) complexity of solving Casida’s equations. Our construction should be useful for the study of excitons in molecular physics and in related areas where χ0 is a crucial ingredient.
Show PACS
31.15.E- Density-functional theory
33.20.-t Molecular spectra

A selection rule for molecular conduction

P. W. Fowler, B. T. Pickup, T. Z. Todorova, and W. Myrvold

J. Chem. Phys. 131, 044104 (2009); http://dx.doi.org/10.1063/1.3182849 (7 pages) | Cited 6 times

Online Publication Date: 22 July 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Conditions for transmission of a π-conjugated molecular conductor are derived within the source and sink potential approach in terms of numbers of nonbonding levels of four graphs: The molecular graph G and the three vertex-deleted subgraphs obtained by removing one or both contact vertices. For all bipartite and most nonbipartite G, counting nonbonding levels gives a simple necessary and sufficient condition for conduction at the Fermi level. The exceptional case is where G is nonbipartite and all four graphs have the same number of nonbonding levels; then, an auxiliary requirement involving tail coefficients of the four characteristic polynomials must also be checked.
Show PACS
85.65.+h Molecular electronic devices
71.20.-b Electron density of states and band structure of crystalline solids

Relative abundance and structure of chaotic behavior: The nonpolynomial Belousov–Zhabotinsky reaction kinetics

Joana G. Freire, Richard J. Field, and Jason A. C. Gallas

J. Chem. Phys. 131, 044105 (2009); http://dx.doi.org/10.1063/1.3168400 (8 pages) | Cited 13 times

Online Publication Date: 22 July 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We report a detailed numerical investigation of the relative abundance of periodic and chaotic oscillations in phase diagrams for the Belousov–Zhabotinsky (BZ) reaction as described by a nonpolynomial, autonomous, three-variable model suggested by Györgyi and Field [Nature (London) 355, 808 (1992) ]. The model contains 14 parameters that may be tuned to produce rich dynamical scenarios. By computing the Lyapunov spectra, we find the structuring of periodic and chaotic phases of the BZ reaction to display unusual global patterns, very distinct from those recently found for gas and semiconductor lasers, for electric circuits, and for a few other familiar nonlinear oscillators. The unusual patterns found for the BZ reaction are surprisingly robust and independent of the parameter explored.
Show PACS
82.40.Bj Oscillations, chaos, and bifurcations
82.20.-w Chemical kinetics and dynamics
82.60.Hc Chemical equilibria and equilibrium constants

Quantum chemistry of quantum dots: Effects of ligands and oxidation

Talgat M. Inerbaev, Artëm E. Masunov, Saiful I. Khondaker, Alexandra Dobrinescu, Andrei-Valentin Plamadă, and Yoshiyuki Kawazoe

J. Chem. Phys. 131, 044106 (2009); http://dx.doi.org/10.1063/1.3135193 (6 pages) | Cited 11 times

Online Publication Date: 23 July 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We report Gaussian basis set density functional theory (DFT) calculations of the structure and spectra of several colloidal quantum dots (QDs) with a (CdSe)n core (n = 6,15,17), that are either passivated by trimethylphosphine oxide ligands, or unpassivated and oxidized. From the ground state geometry optimization results we conclude that trimethylphosphine oxide ligands preserve the wurtzite structure of the QDs. Evaporation of the ligands may lead to surface reconstruction. We found that the number of two-coordinated atoms on the nanoparticle’s surface is the critical parameter defining the optical absorption properties. For (CdSe)15 wurtzite-derived QD this number is maximal among all considered QDs and the optical absorption spectrum is strongly redshifted compared to QDs with threefold coordinated surface atoms. According to the time-dependent DFT results, surface reconstruction is accompanied by a significant decrease in the linear absorption. Oxidation of QDs destroys the perfection of the QD surface, increases the number of two-coordinated atoms and results in the appearance of an infrared absorption peak close to 700 nm. The vacant orbitals responsible for this near infrared transition have strong Se–O antibonding character. Conclusions of this study may be used in optimization of engineered nanoparticles for photodetectors and photovoltaic devices.
Show PACS
71.70.Ch Crystal and ligand fields
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
78.67.Hc Quantum dots
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion

How to tell when a model Kohn–Sham potential is not a functional derivative

Alex P. Gaiduk and Viktor N. Staroverov

J. Chem. Phys. 131, 044107 (2009); http://dx.doi.org/10.1063/1.3176515 (7 pages) | Cited 7 times

Online Publication Date: 23 July 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A model exchange-correlation potential constructed with Kohn–Sham orbitals should be a functional derivative of some density functional. Several necessary conditions for a functional derivative are discussed including: (i) minimization of the total-energy expression by the ground-state solution of the Kohn–Sham equations, (ii) path independence of the van Leeuwen–Baerends line integral, and (iii) net zero force and zero torque on the density. A number of existing model potentials are checked for these properties and it is found that most of the potentials tested are not functional derivatives. Physical properties obtained from potentials that have no parent functionals are ambiguous and, therefore, should be interpreted with caution.
Show PACS
31.15.eg Exchange-correlation functionals (in current density functional theory)

Can short-range hybrids describe long-range-dependent properties?

Thomas M. Henderson, Artur F. Izmaylov, Giovanni Scalmani, and Gustavo E. Scuseria

J. Chem. Phys. 131, 044108 (2009); http://dx.doi.org/10.1063/1.3185673 (9 pages) | Cited 23 times

Online Publication Date: 23 July 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Long-range-corrected hybrids, which incorporate all of the long-range exact exchange interaction, improve performance for a host of molecular properties. The long-range portion of exact exchange is both computationally and formally problematic in solids, and screened hybrids therefore eliminate it. While screened hybrids give similar results to their parent global hybrids for many molecular properties, one may worry that they perform poorly for those properties that are improved by the long-range-correction procedure. In this paper, we show that at least for the Heyd–Scuseria–Ernzerhof (HSE) screened hybrid, this is not the case; for many properties improved by long-range-correction, screened hybrids and global hybrids deliver essentially the same results. We suggest that this is because screened hybrids and global hybrids have fundamentally the same many-electron self-interaction error. We also introduce some small revisions to our computational implementation of the HSE screened hybrid, and we recommend these revisions for future applications of HSE.
Show PACS
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)

Polarization of one-dimensional periodic systems in a static electric field: Sawtooth potential treatment revisited

Bernard Kirtman, Mauro Ferrero, Michel Rérat, and Michael Springborg

J. Chem. Phys. 131, 044109 (2009); http://dx.doi.org/10.1063/1.3185727 (10 pages) | Cited 3 times

Online Publication Date: 23 July 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Various periodic piecewise linear potentials for extracting the electronic response of an infinite periodic system to a uniform electrostatic field are examined. It is shown that discontinuous potentials, such as the sawtooth, cannot be used for this purpose. Continuous triangular potentials can be successfully employed to determine both even- and odd-order (hyper)polarizabilities, as demonstrated here for the first time, although the permanent dipole moment of the corresponding long finite chain remains out of reach. Moreover, for typical highly polarizable organic systems, the size of the repeated unit has to be much larger than that of the finite system in order to obtain convergence with respect to system size. All results are illustrated both through extensive model calculations and through ab initio calculations on poly- and oligoacetylenes.
Show PACS
31.15.ap Polarizabilities and other atomic and molecular properties
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
36.20.-r Macromolecules and polymer molecules

Exact-exchange kernel of time-dependent density functional theory: Frequency dependence and photoabsorption spectra of atoms

Maria Hellgren and Ulf von Barth

J. Chem. Phys. 131, 044110 (2009); http://dx.doi.org/10.1063/1.3179756 (13 pages) | Cited 9 times

Online Publication Date: 24 July 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
In this work we have calculated excitation energies and photoionization cross sections of Be and Ne in the exact-exchange (EXX) approximation of time-dependent density functional theory (TDDFT). The main focus has been on the frequency dependence of the EXX kernel and on how it affects the spectrum as compared to the corresponding adiabatic approximation. We show that for some discrete excitation energies the frequency dependence is essential to reproduce the results of time-dependent Hartree-Fock theory. Unfortunately, we have found that the EXX approximation breaks down completely at higher energies, producing a response function with the wrong analytic structure and making inner-shell excitations disappear from the calculated spectra. We have traced this failure to the existence of vanishing eigenvalues of the Kohn-Sham non-interacting response function. Based on the adiabatic TDDFT formalism we propose a new way of deriving the Fano parameters of autoionizing resonances.
Show PACS
32.80.Fb Photoionization of atoms and ions
31.15.ee Time-dependent density functional theory
32.80.Zb Autoionization
31.15.xr Self-consistent-field methods

An improved treatment of spectator mode vibrations in reduced dimensional quantum dynamics: Application to the hydrogen abstraction reactions μ+CH4, H+CH4, D+CH4, and CH3+CH4

Simon T. Banks, Christofer S. Tautermann, Sarah M. Remmert, and David C. Clary

J. Chem. Phys. 131, 044111 (2009); http://dx.doi.org/10.1063/1.3177380 (12 pages) | Cited 7 times

Online Publication Date: 24 July 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A method for projecting chemical reaction surface coordinates from a Hessian in curvilinear internal coordinates has recently been developed. Here we introduce a modification to this approach which allows for analytical evaluation of the necessary coordinate derivatives, thus reducing the number of ab initio calculations required. We apply this method to the determination of spectator mode frequencies and zero-point energies for the series of hydrogen abstraction reactions X+CH4→XH+CH3, X = muonium (μ), H, D, CH3. Comparison of these frequencies with those obtained using rectilinear coordinates allows us to examine how the mass of X affects the coordinate sensitivity of the spectator modes. We carry out two-dimensional quantum reactive scattering calculations for these reactions to highlight instances where the choice of coordinates may have a significant impact on the evaluated thermal rate constants.
Show PACS
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.20.Xr Quantum effects in rate constants (tunneling, resonances, etc.)

Quasienergy formulation of damped response theory

Kasper Kristensen, Joanna Kauczor, Thomas Kjærgaard, and Poul Jørgensen

J. Chem. Phys. 131, 044112 (2009); http://dx.doi.org/10.1063/1.3173828 (33 pages) | Cited 10 times

Online Publication Date: 24 July 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We present a quasienergy-based formulation of damped response theory where a common effective lifetime parameter has been introduced for all excited states in terms of complex excitation energies. The introduction of finite excited state lifetimes leads to a set of (complex) damped response equations, which have the same form to all orders in the perturbation. An algorithm is presented for solving the damped response equations in Hartree–Fock theory and Kohn–Sham density functional theory. The use of the quasienergy formulation allows us to obtain directly the computationally simplest expressions for damped response functions by applying a set of response parameter elimination rules, which minimize the total number of damped response equations to be solved. In standard response theory broadened absorption spectra are obtained by ad hoc superimposing lineshape functions onto the absorption stick spectra, whereas an empirical lineshape function common to all excitations is an integrated part of damped response theory. By superimposing the lineshape functions inherent in damped response theory onto the stick spectra of standard response theory, we show that the absorption spectra obtained in standard and damped response theory calculations are identical. We demonstrate that damped response theory may be applied to obtain absorption spectra in all frequency ranges, also those that are not readily addressed using standard response theory. This makes damped response theory an effective tool, e.g., for determining absorption spectra for large molecules, where the density of the excited states may be very high, and where standard response theory therefore is not applicable in practice. A thorough comparison is given between our formulation of damped response theory and the formulation by Norman et al. [J. Chem. Phys. 123, 194103 (2005) ].
Show PACS
31.15.xr Self-consistent-field methods
31.15.E- Density-functional theory
33.70.Jg Line and band widths, shapes, and shifts

VARICELLA: A variable-cell direct space method for structure determination from powder diffraction data

Arnaldo Rapallo

J. Chem. Phys. 131, 044113 (2009); http://dx.doi.org/10.1063/1.3189290 (16 pages)

Online Publication Date: 24 July 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A direct space method for structure determination from powder diffraction data is proposed. Employing a hybrid Monte Carlo algorithm for generating the random conformations of a flexible molecular model, and sampling in a modified multicanonical statistical ensemble, it allows for variable cell parameters during an iterative search process. The acceptance-rejection criterion involves both a disagreement factor between the calculated and the experimental diffraction profiles and a modified crystal energy so that the space of tentative solutions can be widely explored while maintaining some physical meaningfulness of the proposals. Allowing the cell to be variable requires the zero shift to be treated as an optimizing parameter; this, in turn, requiring the disagreement factor to be based on the Fourier transform of the spectrum. The algorithm is presented in both a serial and a parallel version, the latter presenting several advantages, such as the possibility to probe different structures at a time while keeping them far from each other in the space defined by suitable order parameters. The method is built up and carefully tested by using, as a case study, a crystal of 3-ethyl 2,3-exo-disyndiotactic norbornene heptamer recently determined by single crystal x-ray diffraction techniques.
Show PACS
61.50.Ah Theory of crystal structure, crystal symmetry; calculations and modeling
61.66.Hq Organic compounds

Charge conservation in electronegativity equalization and its implications for the electrostatic properties of fluctuating-charge models

Jiahao Chen and Todd J. Martínez

J. Chem. Phys. 131, 044114 (2009); http://dx.doi.org/10.1063/1.3183167 (3 pages) | Cited 2 times

Online Publication Date: 24 July 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
An analytical solution of fluctuating-charge models using Gaussian elimination allows us to isolate the contribution of charge conservation effects in determining the charge distribution. We use this analytical solution to calculate dipole moments and polarizabilities and show that charge conservation plays a critical role in maintaining the correct translational invariance of the electrostatic properties predicted by these models.
Show PACS
31.15.xv Molecular dynamics and other numerical methods
34.70.+e Charge transfer
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
41.20.Cv Electrostatics; Poisson and Laplace equations, boundary-value problems

Quantum Monte Carlo ground state energies for the atoms Li through Ar

E. Buendía, F. J. Gálvez, P. Maldonado, and A. Sarsa

J. Chem. Phys. 131, 044115 (2009); http://dx.doi.org/10.1063/1.3187526 (7 pages) | Cited 4 times

Online Publication Date: 27 July 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
All-electron quantum Monte Carlo energies are reported for the ground state of the atoms Li to Ar. The present work is mainly focused on the atoms Na to Ar as well as in those that have a stronger multiconfiguration nature, i.e., Be, B, and C and Mg, Al, and Si. Explicitly correlated wave functions with a single configuration model function times a Jastrow factor are employed for all of the atoms studied. The accuracy obtained for the atoms Na to Ar is similar to that reached for the atoms Li to Ne. In addition, a restricted multiconfiguration expansion has been employed for the atoms Be, B, and C and Mg, Al, and Si obtaining accurate results. Near degeneracy and the effect of other configurations are systematically analyzed for these systems, at both variational and diffusion Monte Carlo levels.
Show PACS
31.15.ve Electron correlation calculations for atoms and ions: ground state
31.15.eg Exchange-correlation functionals (in current density functional theory)
31.15.xt Variational techniques

Frozen Gaussian series representation of the imaginary time propagator theory and numerical tests

Dong H. Zhang, Jiushu Shao, and Eli Pollak

J. Chem. Phys. 131, 044116 (2009); http://dx.doi.org/10.1063/1.3190328 (9 pages)

Online Publication Date: 27 July 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Thawed Gaussian wavepackets have been used in recent years to compute approximations to the thermal density matrix. From a numerical point of view, it is cheaper to employ frozen Gaussian wavepackets. In this paper, we provide the formalism for the computation of thermal densities using frozen Gaussian wavepackets. We show that the exact density may be given in terms of a series, in which the zeroth order term is the frozen Gaussian. A numerical test of the methodology is presented for deep tunneling in the quartic double well potential. In all cases, the series is observed to converge. The convergence of the diagonal density matrix element is much faster than that of the antidiagonal one, suggesting that the methodology should be especially useful for the computation of partition functions. As a by product of this study, we find that the density matrix in configuration space can have more than two saddle points at low temperatures. This has implications for the use of the quantum instanton theory.
Show PACS
05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion
02.30.Tb Operator theory
05.60.Gg Quantum transport
03.65.Fd Algebraic methods
02.10.Yn Matrix theory
02.60.Dc Numerical linear algebra

A Hirshfeld interpretation of the charge, spin distribution, and polarity of the dipole moment of the open shell (3Σ−) nitrogen halides: NF, NCl, and NBr

James F. Harrison

J. Chem. Phys. 131, 044117 (2009); http://dx.doi.org/10.1063/1.3190330 (12 pages) | Cited 3 times

Online Publication Date: 27 July 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We calculated the dipole moment function for the ground 3Σ−(mS = +1) state of the open shell molecules, NF, NCl, and NBr, and analyzed it in terms of the charge and spin distribution and the induced atomic dipoles using the Hirshfeld partitioning of the electron density. The smallest dipole moment (0.026ea0) obtains with NF, in which the atoms have the largest difference in electronegativity, while the dipole moments in NCl and NBr are 0.441ea0 and 0.506ea0, respectively. All dipoles have the N−X+ polarity. In the σ system α spin electrons flow from N to the halogen while β spin electrons flow in the opposite direction and interestingly from both the σ and the π systems of the halogen to the σ system of N. In NF the number of β spins lost by F is essentially equal to the number of α spins gained and the atomic charges are essentially 0. The small dipole in NF is the result of a slight imbalance in the induced atomic dipoles. For NCl and NBr the halogen loses more β spins than it gains α spins resulting in the polarity N−X+. It is interesting that at equilibrium N gained electrons in the π system while the halogen lost π electrons relative to the separated atoms. This however is not back donation in the usual sense because the electrons gained by N have α spin while those lost by the halogen have β spin. Detailed examination of the spin flow shows that the excess α electrons in the π system of N come from an intra-atomic transfer from the N σ system. The induced atomic dipole moments essentially cancel at all internuclear separations and the polarity of the dipole moment accurately reflects the molecular charge distribution.
Show PACS
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
31.15.-p Calculations and mathematical techniques in atomic and molecular physics
34.20.Gj Intermolecular and atom-molecule potentials and forces

Explicitly correlated combined coupled-cluster and perturbation methods

Toru Shiozaki, Edward F. Valeev, and So Hirata

J. Chem. Phys. 131, 044118 (2009); http://dx.doi.org/10.1063/1.3193463 (12 pages) | Cited 15 times

Online Publication Date: 27 July 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Coupled-cluster singles and doubles (CCSD) or coupled-cluster singles, doubles, and triples (CCSDT) with noniterative, perturbation corrections for higher-order excitations have been extended to include the basis functions that explicitly depend on interelectronic distances (r12) in the wave function expansions with the aim of dramatically accelerating the basis-set convergence of correlation energies. The extension has been based on the so-called R12 (or F12) scheme and applied to a second-order triples correction to CCSD [CCSD(2)T-R12], a second-order triples and quadruples correction to CCSD [CCSD(2)TQ-R12], a third-order triples correction to CCSD [CCSD(3)T-R12], and a second-order quadruples correction to CCSDT [CCSDT(2)Q-R12]. A simplified R12 treatment suggested by Fliegl et al. [J. Chem. Phys. 122, 084107 (2005)] has been combined with some of these methods, introducing CCSD(2)T(R12) and CCSD(2)TQ(R12). The CCSD(T)-R12 method has also been developed as an approximation to CCSD(2)T-R12. These methods have been applied to dissociation of hydrogen fluoride and double dissociation of water. For the molecules at their equilibrium geometries, molecular properties predicted by these methods converge extremely rapidly toward the complete-correlation, complete-basis-set limits with respect to the cluster excitation rank, perturbation order, and basis-set size. Although the R12 scheme employed in this work does not improve the basis-set convergence of connected triples or quadruples corrections, the basis-set truncation errors in these contributions have roughly the same magnitude as small residual basis-set truncation errors in the connected singles and doubles contributions even in the dissociation of hydrogen fluoride. In the double dissociation of water, the basis-set truncation errors in the connected triples contribution can be a few times as great as those in the connected singles and doubles contributions.
Show PACS
31.15.bw Coupled-cluster theory
31.15.xp Perturbation theory
31.30.-i Corrections to electronic structure
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.15.Fm Bond strengths, dissociation energies

Correlation-induced corrections to the band structure of boron nitride: A wave-function-based approach

A. Stoyanova, L. Hozoi, P. Fulde, and H. Stoll

J. Chem. Phys. 131, 044119 (2009); http://dx.doi.org/10.1063/1.3177010 (20 pages) | Cited 4 times

Online Publication Date: 27 July 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We present a systematic study of the correlation-induced corrections to the electronic band structure of zinc-blende BN. Our investigation employs an ab initio wave-function-based local Hamiltonian approach which offers a rigorous theoretical framework for the calculation of the polarization and local charge redistribution effects around an extra electron or hole placed into the conduction or valence bands of semiconducting and insulating materials. Moreover, electron correlations beyond relaxation and polarization can be readily incorporated. The electron correlation treatment is performed on finite clusters. In conducting our study, we make use of localized Wannier functions and embedding potentials derived explicitly from prior periodic Hartree–Fock calculations. The on-site and nearest-neighbor charge relaxations bring corrections of several eV to the Hartree–Fock band gap. Additional corrections are caused by long-range polarization effects. In contrast, the dispersion of the Hartree–Fock bands is marginally affected by electron correlations. Our final result for the fundamental gap of zinc-blende BN compares well with that derived from soft x-ray experiments at the B and N K-edges.
Show PACS
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)

Exact rate calculations by trajectory parallelization and tilting

Eric Vanden-Eijnden and Maddalena Venturoli

J. Chem. Phys. 131, 044120 (2009); http://dx.doi.org/10.1063/1.3180821 (7 pages) | Cited 10 times

Online Publication Date: 27 July 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A sampling procedure to compute exactly the rate of activated processes arising in systems at equilibrium or nonequilibrium steady state is presented. The procedure is a generalization of the method proposed in [ A. Warmflash et al., J. Chem. Phys. 127, 154112 (2007) ; A. Dickson et al., J. Chem. Phys. 130, 074104 (2009) ] in which one performs simulations restricted into cells by using a reinjection rule at the boundaries of the cells which is consistent with the exact probability fluxes through these boundaries. Our generalization uses results from transition path theory which indicate how to tilt the dynamics to calculate reaction rates.
Show PACS
82.20.Pm Rate constants, reaction cross sections, and activation energies
02.50.-r Probability theory, stochastic processes, and statistics

Computation of molecular vibrational frequencies using anomalous harmoniclike potentials

Xiangzhu Li and Josef Paldus

J. Chem. Phys. 131, 044121 (2009); http://dx.doi.org/10.1063/1.3192100 (12 pages) | Cited 2 times

Online Publication Date: 27 July 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The instabilities of Hartree–Fock (HF) solutions at or near the equilibrium geometry of symmetric molecular species imply the existence of broken-symmetry solutions having a lower energy than the corresponding symmetry-adapted ones. Moreover, the distortion of the nuclear framework along the normal modes that are implied by such broken-symmetry solutions results in an anomalous or even singular behavior in the corresponding cuts of the potential energy surface (PES). Using such HF solutions as a reference, these anomalies propagate to a post-HF level and make it impossible to determine reliable harmonic or fundamental vibrational frequencies for such modes by relying on either numerical or analytical differentiation of the PES, requiring instead a numerical integration of the Schrödinger equation for the nuclear motion. This, in turn, requires a detailed knowledge on the PES in a wide range of geometries, necessitating a computation of the potential energy function in a large number of points. We present an alternative approach to this problem, referred to as the integral averaging method (IAM), which facilitates this task by significantly reducing the number of geometries for which one has to compute the potential energy while yielding results of practically the same accuracy as the solution of the Schrödinger equation. The IAM is applied to several ABA-type triatomics and to the allyl radical, whose asymmetric stretching mode potential suffers from an anomalous behavior due to the spin-preserving instabilities in restricted open-shell HF solutions.
Show PACS
33.20.Tp Vibrational analysis
31.15.xr Self-consistent-field methods
31.50.-x Potential energy surfaces
33.15.Bh General molecular conformation and symmetry; stereochemistry

Spin-orbit coupling effects in dihydrides of third-row transition elements. II. Interplay of nonadiabatic coupling in the dissociation path of rhenium dihydride

Shiro Koseki, Noriyuki Shimakura, Yuichi Fujimura, Toshio Asada, and Hirohiko Kono

J. Chem. Phys. 131, 044122 (2009); http://dx.doi.org/10.1063/1.3176510 (8 pages) | Cited 2 times

Online Publication Date: 27 July 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
This is the second paper in a series of investigations on spin-orbit coupling (SOC) effects in dihydrides of third-row transition elements. The dissociation path of rhenium dihydride was explored using the multiconfiguration self-consistent-field method followed by diagonalization of SOC matrices, in which the Stevens–Basch–Krauss–Jasien–Cundari (SBKJC) basis sets were employed after adding one set of polarization functions for each atom. The most stable rhenium dihydride has a linear structure and its ground state is 6Σg+. Both C2v and Cs dissociation paths into a Re atom and a hydrogen molecule (Re(6S)+H2(1Σg+)) were explored on the potential energy curves of low-lying states. A relatively high energy barrier was obtained along the C2v path and two conical intersections were found at the H–Re–H angles of 29.8° and 96.1° along the C2v path. Since it was revealed that the geometrical deformation to Cs symmetry at the H–Re–H angle of 29.8° does not provide explicit lowering of the energy barrier for the dissociation, even after considering nonadiabatic couplings (NACs) in the neighborhood of the conical intersections, it can be concluded that the most feasible path is hopping from the lowest 6A1 state to the lowest 6B2 state at the H–Re–H angle of 96.1° followed by hopping from the lowest 6B2 state back to the lowest 6A1 state at the H–Re–H angle of 29.8°, where the latter crossing point is the highest in energy along this path. Thus, when the molecular system can reach the areas of these crossing points, the molecular system hops from one of the states to another owing to NAC or SOC effects; especially, SOC effects become important at the crossing point with C2v symmetry.
Show PACS
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.20.Kh Potential energy surfaces for chemical reactions
31.15.xr Self-consistent-field methods
82.20.Hf Product distribution
31.50.Gh Surface crossings, non-adiabatic couplings

Heterogeneous conductorlike solvation model

Dejun Si and Hui Li

J. Chem. Phys. 131, 044123 (2009); http://dx.doi.org/10.1063/1.3187527 (8 pages) | Cited 2 times

Online Publication Date: 27 July 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A heterogeneous conductorlike solvation model (conductorlike screening model/conductorlike polarizable continuum model) that uses different local effective dielectrics for different portions of the solute cavity surface is implemented for quantum chemical Hartree–Fock and Kohn–Sham methods. A variational treatment is used to form the heterogeneous solvation operator, so a simple analytic expression of the energy gradients, which are vital for geometry optimization and molecular dynamics simulation, is derived and implemented. Using the new Fixed Points with Variable Areas surface tessellation scheme, continuous and smooth potential energy surfaces as well as analytic gradients are obtained for this heterogeneous model. Application of the heterogeneous solvation model to a realistic quantum model consisting of 101 atoms for the type-1 Cu center in rusticyanin shows that the desolvation due to protein burial can likely raise the reduction potential by ∼ 200 mV and, including the heterogeneity in geometry optimization, can likely affect the results by ∼ 2 kcal/mol or ∼ 70 mV.
Show PACS
82.30.Nr Association, addition, insertion, cluster formation
87.15.R- Reactions and kinetics
82.20.Kh Potential energy surfaces for chemical reactions
82.20.Fd Collision theories; trajectory models
82.20.Db Transition state theory and statistical theories of rate constants
77.22.Ch Permittivity (dielectric function)
Page 1 of 5 Pages Next Page | Jump to Page
Close

Google Calendar

ADVERTISEMENT

Your Recent History Recent History Help

Recently Viewed

  1. Charge-transfer character of excitons in poly[2,7-(9,9-di-n-octylfluorene)(1−x)-co-4,7-(2,1,3-benzothiadiazole)(x)]
  2. Electronic structure of aromatic amino acids studied by soft x-ray spectroscopy
  3. Nearly symmetrical proteins: Folding pathways and transition states
  4. On the anisotropy of lattice polymers
  5. Koopmans’ springs to life
Go to AIP Home
Copyright © American Institute of Physics
close