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

14 Aug 2008

Volume 129, Issue 6, Articles (06xxxx)

Page 1 of 3 Pages Next Page | Jump to Page
back to top
RSS Feeds

Phase-separation transition in liquid mixtures near curved charged objects

Gilad Marcus, Sela Samin, and Yoav Tsori

J. Chem. Phys. 129, 061101 (2008); http://dx.doi.org/10.1063/1.2965906 (4 pages) | Cited 12 times

Online Publication Date: 8 August 2008

Full Text: | Download PDF

Show Abstract
We study the thermodynamic behavior of nonpolar liquid mixtures in the vicinity of curved charged objects, such as electrodes or charged colloids. There is a critical value of charge (or potential), above which a phase-separation transition occurs, and the interface between high- and low-dielectric constant components becomes sharp. Analytical and numerical composition profiles are given, and the equilibrium front location as a function of charge or voltage is found. We further employ a simple Cahn–Hilliard type equation to study the dynamics of phase separation in spatially nonuniform electric fields. We find an exponential temporal relaxation of the demixing front location. We give the dependence of the steady-state location and characteristic time on the charge, mixture composition and ambient temperature.
Show PACS
61.25.-f Studies of specific liquid structures
64.75.-g Phase equilibria
back to top
RSS Feeds
back to top Theoretical Methods and Algorithms

Reappraisal of cis effect in 1,2-dihaloethenes: An improved virtual orbital multireference approach

Rajat K. Chaudhuri, Jeff R. Hammond, Karl F. Freed, Sudip Chattopadhyay, and Uttam Sinha Mahapatra

J. Chem. Phys. 129, 064101 (2008); http://dx.doi.org/10.1063/1.2958284 (9 pages) | Cited 7 times

Online Publication Date: 8 August 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Computed relative stabilities for isomers of 1,2-difluoroethene and 1,2-dichloroethene isomers are compared with predictions based on chemical hardness (η) and electrophilicity (ω) using the principles of maximum hardness and minimum electrophilicity. The chemical hardness and electrophilicity deduced either from improved virtual orbital (IVO) energies or from correlated treatments correctly predict that cis 1,2-difluoroethene and 1,2-dichloroethene are energetically more stable than the corresponding trans isomers, and the ground state energies from multireference perturbation theory with IVO orbitals agree with these predictions. However, when the same quantities are computed using Hartree–Fock orbitals, serious inconsistencies between the two approaches emerge in predicting the stability of the isomers of the 1,2-dihaloethenes. The present study clearly demonstrates that the IVO energies are appropriate for the computation of hardness related parameters, notably the chemical hardness and electrophilicity. Moreover, the IVO methods also provide smooth potential energy curves for the cis-trans isomerization of the two 1,2-dihaloethenes.
Show PACS
82.30.Qt Isomerization and rearrangement
82.20.Kh Potential energy surfaces for chemical reactions

A gradient-directed Monte Carlo approach to molecular design

Xiangqian Hu, David N. Beratan, and Weitao Yang

J. Chem. Phys. 129, 064102 (2008); http://dx.doi.org/10.1063/1.2958255 (9 pages) | Cited 10 times

Online Publication Date: 8 August 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The recently developed linear combination of atomic potentials (LCAP) approach [ M. Wang et al., J. Am. Chem. Soc. 128, 3228 (2006) ] allows continuous optimization in a discrete chemical space, and thus is useful in the design of molecules for targeted properties. To address further challenges arising from the rugged, continuous property surfaces in the LCAP approach, we develop a gradient-directed Monte Carlo (GDMC) strategy as an augmentation to the original LCAP optimization method. The GDMC method retains the power of exploring molecular space by utilizing local gradient information computed from the LCAP approach to jump between discrete molecular structures. It also allows random MC moves to overcome barriers between local optima on property surfaces. The combined GDMC–LCAP approach is demonstrated here for optimizing nonlinear optical properties in a class of donor-acceptor substituted benzene and porphyrin frameworks. Specifically, one molecule with four nitrogen atoms in the porphyrin ring was found to have a larger first hyperpolarizability than structures with the conventional porphyrin motif.
Show PACS
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
33.15.Bh General molecular conformation and symmetry; stereochemistry
02.70.Uu Applications of Monte Carlo methods
02.60.Pn Numerical optimization

Monte Carlo configuration interaction predictions for the electronic spectra of Ne, CH2, C2, N2, and H2O compared to full configuration interaction calculations

W. Győrffy, R. J. Bartlett, and J. C. Greer

J. Chem. Phys. 129, 064103 (2008); http://dx.doi.org/10.1063/1.2965529 (10 pages) | Cited 7 times

Online Publication Date: 8 August 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Singlet and triplet electronic excitation energies have been calculated for Ne, CH2, C2, N2, and H2O using the Monte Carlo configuration interaction (CI) method. We find that excitation energies can be predicted to within a few tens of meV of full CI (FCI) results using expansions consisting of only a few thousand configuration state functions as compared to the O(108) configurations occurring in the corresponding FCI expansions. The method provides a consistently accurate and balanced description of electronic excitations with accuracy for small molecular systems comparable to the equation-of-motion coupled cluster method with full triples.
Show PACS
31.15.vj Electron correlation calculations for atoms and ions: excited states
31.10.+z Theory of electronic structure, electronic transitions, and chemical binding

The spin-flip extended single excitation configuration interaction method

David Casanova and Martin Head-Gordon

J. Chem. Phys. 129, 064104 (2008); http://dx.doi.org/10.1063/1.2965131 (12 pages) | Cited 10 times

Online Publication Date: 8 August 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
An extension of the spin-flip single excitation configuration interaction (SF-CIS) method is introduced. The extension, abbreviated as SF-XCIS, includes all configurations in which no more than one virtual level of the high spin triplet reference becomes occupied and no more than one doubly occupied level becomes vacant. The number of such configurations is quadratic with molecule size, and the method is implemented in a direct algorithm whose cost scales in the same way with molecule size as CIS itself, thus permitting applications to large systems. Starting from a spin restricted triplet determinant, SF-XCIS yields spin-pure singlet, triplet, and quintet states, and treats both half-occupied reference orbitals in a fully balanced way to allow application to strongly correlated problems. Tests on bond dissociation in the HF molecule, the torsional potential of ethylene, and excited states of polyenes show encouraging improvements using SF-XCIS compared to SF-CIS and a previously suggested extension, the spin-complete CIS model.
Show PACS
31.15.V- Electron correlation calculations for atoms, ions and molecules
33.15.Fm Bond strengths, dissociation energies
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis

Adiabatic connection forms in density functional theory: H2 and the He isoelectronic series

Michael J. G. Peach, Adam M. Miller, Andrew M. Teale, and David J. Tozer

J. Chem. Phys. 129, 064105 (2008); http://dx.doi.org/10.1063/1.2965531 (7 pages) | Cited 6 times

Online Publication Date: 11 August 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Full configuration interaction (FCI) data are used to quantify the accuracy of approximate adiabatic connection (AC) forms in describing two challenging problems in density functional theory—the singlet ground state potential energy curve of H2 in a restricted formalism and the energies of the helium isoelectronic series, H− to Ne8+. For H2, an exponential-based form yields a potential energy curve that is virtually indistinguishable from the FCI curve, eliminating the unphysical barrier to dissociation observed previously with a [1,1]-Padé-based form and with the random phase approximation. For the helium isoelectronic series, the Padé-based form gives the best overall description, followed by the exponential form, with errors that are orders of magnitude smaller than those from a standard hybrid functional. Particular attention is paid to the limiting behavior of the AC forms with increasing bond distance in H2 and increasing atomic number in the isoelectronic series; several forms describe both limits correctly. The study illustrates the very high quality results that can be obtained using exchange-correlation functionals based on simple AC forms, when near-exact data are used to determine the parameters in the forms.
Show PACS
31.15.E- Density-functional theory
31.15.ve Electron correlation calculations for atoms and ions: ground state
31.50.Bc Potential energy surfaces for ground electronic states
33.15.Dj Interatomic distances and angles

On a partial differential equation method for determining the free energies and coexisting phase compositions of ternary mixtures from light scattering data

David S. Ross, George M. Thurston, and Carl V. Lutzer

J. Chem. Phys. 129, 064106 (2008); http://dx.doi.org/10.1063/1.2937902 (11 pages) | Cited 2 times

Online Publication Date: 11 August 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
In this paper we present a method for determining the free energies of ternary mixtures from light scattering data. We use an approximation that is appropriate for liquid mixtures, which we formulate as a second-order nonlinear partial differential equation. This partial differential equation (PDE) relates the Hessian of the intensive free energy to the efficiency of light scattering in the forward direction. This basic equation applies in regions of the phase diagram in which the mixtures are thermodynamically stable. In regions in which the mixtures are unstable or metastable, the appropriate PDE is the nonlinear equation for the convex hull. We formulate this equation along with continuity conditions for the transition between the two equations at cloud point loci. We show how to discretize this problem to obtain a finite-difference approximation to it, and we present an iterative method for solving the discretized problem. We present the results of calculations that were done with a computer program that implements our method. These calculations show that our method is capable of reconstructing test free energy functions from simulated light scattering data. If the cloud point loci are known, the method also finds the tie lines and tie triangles that describe thermodynamic equilibrium between two or among three liquid phases. A robust method for solving this PDE problem, such as the one presented here, can be a basis for optical, noninvasive means of characterizing the thermodynamics of multicomponent mixtures.
Show PACS
65.20.-w Thermal properties of liquids
64.75.-g Phase equilibria

Building Markov state models along pathways to determine free energies and rates of transitions

Albert C. Pan and Benoît Roux

J. Chem. Phys. 129, 064107 (2008); http://dx.doi.org/10.1063/1.2959573 (8 pages) | Cited 21 times

Online Publication Date: 12 August 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
An efficient method is proposed for building Markov models with discrete states able to accurately describe the slow relaxation of a complex system with two stable conformations. First, the reaction pathway described by a set of collective variables between the two stable states is determined using the string method with swarms of trajectories. Then, short trajectories are initiated at different points along this pathway to build the state-to-state transition probability matrix. It is shown, using a model system, how this strategy makes it possible to use trajectories that are significantly shorter than the slowest relaxation time to efficiently build a reliable and accurate Markov model. Extensions of the method to multiple pathways, as well as some common pitfalls arising from poorly relaxed paths or an inappropriate choice of collective variables, are illustrated and discussed.
Show PACS
82.20.Rp State to state energy transfer
82.60.-s Chemical thermodynamics
82.20.Kh Potential energy surfaces for chemical reactions
82.20.Wt Computational modeling; simulation

Developing ab initio quality force fields from condensed phase quantum-mechanics/molecular-mechanics calculations through the adaptive force matching method

Omololu Akin-Ojo, Yang Song, and Feng Wang

J. Chem. Phys. 129, 064108 (2008); http://dx.doi.org/10.1063/1.2965882 (11 pages) | Cited 16 times

Online Publication Date: 12 August 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A new method called adaptive force matching (AFM) has been developed that is capable of producing high quality force fields for condensed phase simulations. This procedure involves the parametrization of force fields to reproduce ab initio forces obtained from condensed phase quantum-mechanics/molecular-mechanics (QM/MM) calculations. During the procedure, the MM part of the QM/MM is iteratively improved so as to approach ab initio quality. In this work, the AFM method has been tested to parametrize force fields for liquid water so that the resulting force fields reproduce forces calculated using the ab initio MP2 and the Kohn–Sham density functional theory with the Becke–Lee–Yang–Parr (BLYP) and Becke three-parameter LYP (B3LYP) exchange correlation functionals. The AFM force fields generated in this work are very simple to evaluate and are supported by most molecular dynamics (MD) codes. At the same time, the quality of the forces predicted by the AFM force fields rivals that of very expensive ab initio calculations and are found to successfully reproduce many experimental properties. The site-site radial distribution functions (RDFs) obtained from MD simulations using the force field generated from the BLYP functional through AFM compare favorably with the previously published RDFs from Car–Parrinello MD simulations with the same functional. Technical aspects of AFM such as the optimal QM cluster size, optimal basis set, and optimal QM method to be used with the AFM procedure are discussed in this paper.
Show PACS
31.15.ap Polarizabilities and other atomic and molecular properties
33.15.Mt Rotation, vibration, and vibration-rotation constants
31.15.eg Exchange-correlation functionals (in current density functional theory)
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
61.20.Ja Computer simulation of liquid structure

Density functional restricted-unrestricted approach for nonlinear properties: Application to electron paramagnetic resonance parameters of square planar copper complexes

Zilvinas Rinkevicius, Katia Julia de Almeida, and Olav Vahtras

J. Chem. Phys. 129, 064109 (2008); http://dx.doi.org/10.1063/1.2964102 (17 pages) | Cited 3 times

Online Publication Date: 12 August 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The density functional restricted-unrestricted approach for treatments of spin polarization effects in molecular properties using spin restricted Kohn–Sham theory has been extended from linear to nonlinear properties. It is shown that the spin polarization contribution to a nonlinear property has the form of a quadratic response function that includes the zero-order Kohn–Sham operator, in analogy to the lower order case where the spin polarization correction to an expectation value has the form of a linear response function. The developed approach is used to formulate new schemes for computation of electronic g-tensors and hyperfine coupling constants, which include spin polarization effects within the framework of spin restricted Kohn–Sham theory. The proposed computational schemes are in the present work employed to study the spin polarization effects on electron paramagnetic resonance spin Hamiltonian parameters of square planar copper complexes. The obtained results indicate that spin polarization gives rise to sizable contributions to the hyperfine coupling tensor of copper in all investigated complexes, while the electronic g-tensors of these complexes are only marginally affected by spin polarization and other factors, such as choice of exchange-correlation functional or molecular structures, will have more pronounced impact on the accuracy of the results.
Show PACS
33.35.+r Electron resonance and relaxation
31.15.eg Exchange-correlation functionals (in current density functional theory)
31.15.ej Spin-density functionals
33.15.Pw Fine and hyperfine structure

Path integral calculation of free energies: Quantum effects on the melting temperature of neon

R. Ramírez, C. P. Herrero, A. Antonelli, and E. R. Hernández

J. Chem. Phys. 129, 064110 (2008); http://dx.doi.org/10.1063/1.2966006 (11 pages) | Cited 7 times

Online Publication Date: 12 August 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The path integral formulation has been combined with several methods to determine free energies of quantum many-body systems, such as adiabatic switching and reversible scaling. These techniques are alternatives to the standard thermodynamic integration method. A quantum Einstein crystal is used as a model to demonstrate the accuracy and reliability of these free energy methods in quantum simulations. Our main interest focuses on the calculation of the melting temperature of Ne at ambient pressure, taking into account quantum effects in the atomic dynamics. The free energy of the solid was calculated by considering a quantum Einstein crystal as reference state, while for the liquid, the reference state was defined by the classical limit of the fluid. Our findings indicate that, while quantum effects in the melting temperature of this system are small, they still amount to about 6% of the melting temperature, and are therefore not negligible. The particle density as well as the melting enthalpy and entropy of the solid and liquid phases at coexistence is compared to results obtained in the classical limit and also to available experimental data.
Show PACS
05.70.Fh Phase transitions: general studies
05.70.Ce Thermodynamic functions and equations of state
05.30.-d Quantum statistical mechanics

Optimization of augmentation functions for correlated calculations of spin-spin coupling constants and related properties

Udo Benedikt, Alexander A. Auer, and Frank Jensen

J. Chem. Phys. 129, 064111 (2008); http://dx.doi.org/10.1063/1.2962973 (8 pages) | Cited 13 times

Online Publication Date: 12 August 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A new hierarchy of augmented basis sets optimized for the calculation of molecular properties such as indirect spin-spin coupling constants is presented. Based on the Dunning hierarchy of cc-pVXZ (X = D, T, Q, and 5) basis sets augmentation functions with tight exponents have been optimized for coupled-cluster calculations of indirect spin-spin coupling constants. The optimal exponents for these tight functions have been obtained by optimizing the sum of the absolute values of all contributions to the coupling constant. On the basis of a series of test cases (CO, HF, N2, F2, H2O, NH3, and CH4) we propose a set of tight s, p, and d functions to be added to the uncontracted Dunning basis sets, and, subsequently, to recontract. The resulting ccJ-pVXZ (X = D, T, Q, and 5) basis sets demonstrate excellent cost efficiency in benchmark calculations. These new basis sets should generally be applicable for the calculation of spin-spin coupling constants and other properties that have a strong dependence on powers of 1/r or even contain a delta distribution for correlated ab initio methods.
Show PACS
31.15.V- Electron correlation calculations for atoms, ions and molecules
31.15.bw Coupled-cluster theory
31.15.A- Ab initio calculations

Restoring the size consistency of multireference configuration interactions through class dressings: Applications to ground and excited states

Nadia Ben Amor, Daniel Maynau, Jean-Paul Malrieu, and Antonio Monari

J. Chem. Phys. 129, 064112 (2008); http://dx.doi.org/10.1063/1.2938371 (10 pages) | Cited 10 times

Online Publication Date: 13 August 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The present paper presents a revised version of a size-consistency correction to the multireference configuration interaction techniques previously proposed by Szalay et al. [J. Phys. Chem. 100, 6288 (1996)]. The method assumes a complete active space reference space and separates the nonreference determinants in several classes according to their number of inactive holes and particles. The correction is formulated as a dressing of the diagonal energies of these determinants, which depends on their class, as originally proposed by Ruttink et al. [J. Chem. Phys. 94, 7212 (1991)]. The exclusion principle violating corrections are evaluated through a simple counting of the various excitation processes which remain possible on each class. The efficiency of the method has been tested on a series of multireference problems for which full configuration interaction results are available (OH2 bond breaking, Be insertion in H2, excited states of CH2). The dressing of a given state not only provides excellent results for this state but also provides accurate excited roots. The efficiency of state-specific dressings is dramatic. The adaptation of this proposal to difference-dedicated configuration interactions can be extremely fruitful, as illustrated in the calculation of the 1 1Ag-11Bu(π−>π*) transition energy of the trans-butadiene molecule.
Show PACS
32.80.Rm Multiphoton ionization and excitation to highly excited states
31.50.Bc Potential energy surfaces for ground electronic states

Closed-shell coupled-cluster theory with spin-orbit coupling

Fan Wang, Jürgen Gauss, and Christoph van Wüllen

J. Chem. Phys. 129, 064113 (2008); http://dx.doi.org/10.1063/1.2968136 (7 pages) | Cited 8 times

Online Publication Date: 13 August 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A two-component closed-shell coupled-cluster (CC) approach using relativistic effective core potentials with spin-orbit coupling included in the post-Hartree–Fock treatment is proposed and implemented at the CC singles and doubles (CCSD) level as well as at the CCSD level augmented by a perturbative treatment of triple excitations [CCSD(T)]. The latter invokes as an additional approximation the neglect of the occupied-occupied and virtual-virtual blocks of the spin-orbit coupling matrix in order to avoid the iterative N7 steps in the treatment of triple excitations. The computational effort of the implemented two-component CC methods is about 10–15 times that of its corresponding nonrelativistic counterpart, which needs to be compared to the by a factor of 32 higher cost for fully relativistic schemes and schemes with spin-orbit coupling included already at the Hartree–Fock self-consistent field (HF-SCF) level. This substantial computational saving is due to the use of real molecular orbitals and real two-electron integrals. Results on 5p-, 6p-, and 7p-block element compounds show that the bond lengths and harmonic frequencies obtained with the present two-component CCSD method agree well with those computed with the CCSD approach including spin-orbit coupling at the HF-SCF level even for the 7p-block element compounds. As for the CCSD(T) approach, high accuracy for 5p- and 6p-block element compounds is retained. However, the difference in bond lengths and harmonic frequencies becomes somewhat more pronounced for the 7p-block element compounds.
Show PACS
31.15.bw Coupled-cluster theory
31.15.xr Self-consistent-field methods
33.15.Dj Interatomic distances and angles
31.30.J- Relativistic and quantum electrodynamic (QED) effects in atoms, molecules, and ions
31.15.V- Electron correlation calculations for atoms, ions and molecules
31.50.Df Potential energy surfaces for excited electronic states

Molecular-orbital-free algorithm for excited states in time-dependent perturbation theory

Melissa J. Lucero, Anders M. N. Niklasson, Sergei Tretiak, and Matt Challacombe

J. Chem. Phys. 129, 064114 (2008); http://dx.doi.org/10.1063/1.2965535 (8 pages) | Cited 5 times

Online Publication Date: 14 August 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A nonlinear conjugate gradient optimization scheme is used to obtain excitation energies within the random phase approximation (RPA). The solutions to the RPA eigenvalue equation are located through a variational characterization using a modified Thouless functional, which is based upon an asymmetric Rayleigh quotient, in an orthogonalized atomic orbital representation. In this way, the computational bottleneck of calculating molecular orbitals is avoided. The variational space is reduced to the physically-relevant transitions by projections. The feasibility of an RPA implementation scaling linearly with system size N is investigated by monitoring convergence behavior with respect to the quality of initial guess and sensitivity to noise under thresholding, both for well- and ill-conditioned problems. The molecular-orbital-free algorithm is found to be robust and computationally efficient, providing a first step toward large-scale, reduced complexity calculations of time-dependent optical properties and linear response. The algorithm is extensible to other forms of time-dependent perturbation theory including, but not limited to, time-dependent density functional theory.
Show PACS
31.15.xp Perturbation theory
31.15.vj Electron correlation calculations for atoms and ions: excited states

Dihydrogen bond cooperativity in (HCCBeH)n clusters

Ibon Alkorta, José Elguero, and Mohammad Solimannejad

J. Chem. Phys. 129, 064115 (2008); http://dx.doi.org/10.1063/1.2966007 (8 pages) | Cited 5 times

Online Publication Date: 14 August 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A theoretical study has been carried out on the clusters formed by the association of ethynylhydroberyllium (HC ≡ CBeH) monomers. The monomer presents a linear disposition with a dipole moment of 0.94 D. Clusters from two to six monomers have been calculated for three different configurations (linear, cyclic with dihydrogen bonds, and cyclic with hydrogen bonds to the π-cloud), the third one being the most stable. The electronic properties of the clusters have been analyzed by means of the atoms in molecules and natural bond orbitals methodologies. Cooperative effects, similar to the ones described for standard hydrogen bonded clusters, are observed in those configurations where dihydrogen bonds are the main interacting force.
Show PACS
31.15.ae Electronic structure and bonding characteristics
31.15.E- Density-functional theory
31.15.bw Coupled-cluster theory
36.40.-c Atomic and molecular clusters
31.30.jp Electron electric dipole moment
31.15.am Relativistic configuration interaction (CI) and many-body perturbation calculations

Perturbative calculation of Franck–Condon integrals: New hints for a rational implementation

Raffaele Borrelli and Andrea Peluso

J. Chem. Phys. 129, 064116 (2008); http://dx.doi.org/10.1063/1.2967183 (7 pages) | Cited 2 times

Online Publication Date: 14 August 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Perturbative approaches to the mode mixing effects in the calculation of Franck–Condon integrals are analyzed and discussed. The zero order multidimensional Franck–Condon integrals are factorized into products of one-dimensional ones, so that recurrence relations can be used without need of storing a huge number of data. Calculations on model systems show that at the second order of perturbation, the method gives results in very good agreement with the exact ones, even in the case of significantly large Duschinsky effect. The accuracy of the results can be substantially improved by grouping together all those modes which are strongly mixed with each other, usually a few ones, for which Franck–Condon integrals can be computed exactly, and using the perturbative approach for treating the smaller mixing between all the other modes.
Show PACS
31.15.xp Perturbation theory
31.50.Df Potential energy surfaces for excited electronic states
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors

Dual descriptors within the framework of spin-polarized density functional theory

E. Chamorro, P. Pérez, M. Duque, F. De Proft, and P. Geerlings

J. Chem. Phys. 129, 064117 (2008); http://dx.doi.org/10.1063/1.2965594 (9 pages) | Cited 6 times

Online Publication Date: 14 August 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Spin-polarized density functional theory (SP-DFT) allows both the analysis of charge-transfer (e.g., electrophilic and nucleophilic reactivity) and of spin-polarization processes (e.g., photophysical changes arising from electron transitions). In analogy with the dual descriptor introduced by Morell et al. [J. Phys. Chem. A 109, 205 (2005)] , we introduce new dual descriptors intended to simultaneously give information of the molecular regions where the spin-polarization process linking states of different multiplicity will drive electron density and spin density changes. The electronic charge and spin rearrangement in the spin forbidden radiative transitions S0→T(n,π*) and S0→T(π,π*) in formaldehyde and ethylene, respectively, have been used as benchmark examples illustrating the usefulness of the new spin-polarization dual descriptors. These quantities indicate those regions where spin-orbit coupling effects are at work in such processes. Additionally, the qualitative relationship between the topology of the spin-polarization dual descriptors and the vertical singlet triplet energy gap in simple substituted carbene series has been also discussed. It is shown that the electron density and spin density rearrangements arise in agreement with spectroscopic experimental evidence and other theoretical results on the selected target systems.
Show PACS
31.15.ej Spin-density functionals
34.70.+e Charge transfer
31.15.vj Electron correlation calculations for atoms and ions: excited states

Algorithmic dimensionality reduction for molecular structure analysis

W. Michael Brown, Shawn Martin, Sara N. Pollock, Evangelos A. Coutsias, and Jean-Paul Watson

J. Chem. Phys. 129, 064118 (2008); http://dx.doi.org/10.1063/1.2968610 (13 pages) | Cited 7 times

Online Publication Date: 14 August 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Dimensionality reduction approaches have been used to exploit the redundancy in a Cartesian coordinate representation of molecular motion by producing low-dimensional representations of molecular motion. This has been used to help visualize complex energy landscapes, to extend the time scales of simulation, and to improve the efficiency of optimization. Until recently, linear approaches for dimensionality reduction have been employed. Here, we investigate the efficacy of several automated algorithms for nonlinear dimensionality reduction for representation of trans, trans-1,2,4-trifluorocyclo-octane conformation—a molecule whose structure can be described on a 2-manifold in a Cartesian coordinate phase space. We describe an efficient approach for a deterministic enumeration of ring conformations. We demonstrate a drastic improvement in dimensionality reduction with the use of nonlinear methods. We discuss the use of dimensionality reduction algorithms for estimating intrinsic dimensionality and the relationship to the Whitney embedding theorem. Additionally, we investigate the influence of the choice of high-dimensional encoding on the reduction. We show for the case studied that, in terms of reconstruction error root mean square deviation, Cartesian coordinate representations and encodings based on interatom distances provide better performance than encodings based on a dihedral angle representation.
Show PACS
31.15.V- Electron correlation calculations for atoms, ions and molecules
33.15.Bh General molecular conformation and symmetry; stereochemistry
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

Ab initio and direct dynamics study of the reaction of Cl atoms with HOCO

Hua-Gen Yu, Joseph S. Francisco, and James T. Muckerman

J. Chem. Phys. 129, 064301 (2008); http://dx.doi.org/10.1063/1.2965523 (7 pages) | Cited 4 times

Online Publication Date: 8 August 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The reaction of Cl with HOCO has been examined using the coupled-cluster method to locate and optimize the critical points on the ground-state potential energy surface. The results show that the reaction produces the HCl and CO2 products as experimentally observed. The reaction occurs via a HOC(O)Cl intermediate with an estimated heat of formation of −97.8±2.0 kcal/mol. A direct ab initio dynamics method has been used to provide insight into the reaction mechanisms and to determine the thermal rate coefficients in the temperature range of 200–600 K. At room temperature, the thermal rate coefficient is predicted to be 3.0×10−11 cm3 molecule−1 s−1 with an activation energy of −0.2 kcal/mol. Two kinds of reactive trajectories are found. One kind proceeds through short-lived HOC(O)Cl complexes with a lifetime of 310 fs while the other kind occurs via longer-lived intermediates with a lifetime of 1.9 ps.
Show PACS
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.20.Hf Product distribution
82.20.Kh Potential energy surfaces for chemical reactions
82.60.Cx Enthalpies of combustion, reaction, and formation

Calculation of the transport and relaxation properties of methane. I. Shear viscosity, viscomagnetic effects, and self-diffusion

Robert Hellmann, Eckard Bich, Eckhard Vogel, Alan S. Dickinson, and Velisa Vesovic

J. Chem. Phys. 129, 064302 (2008); http://dx.doi.org/10.1063/1.2958279 (13 pages) | Cited 8 times

Online Publication Date: 11 August 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Transport properties of pure methane gas have been calculated in the rigid-rotor approximation using the recently proposed intermolecular potential energy hypersurface [ R. Hellmann et al., J. Chem. Phys. 128, 214303 (2008) ] and the classical-trajectory method. Results are reported in the dilute-gas limit for shear viscosity, viscomagnetic coefficients, and self-diffusion in the temperature range of 80–1500 K. Compared with the best measurements, the calculated viscosity values are about 0.5% too high at room temperature, although the temperature dependence of the calculated values is in very good agreement with experiment between 210 and 390 K. For the shear viscosity, the calculations indicate that the corrections in the second-order approximation and those due to the angular-momentum polarization are small, less than 0.7%, in the temperature range considered. The very good agreement of the calculated values with the experimental viscosity data suggests that the rigid-rotor approximation should be very reasonable for the three properties considered. In general, the agreement for the other measured properties is within the experimental error.
Show PACS
51.10.+y Kinetic and transport theory of gases
51.60.+a Magnetic properties
51.20.+d Viscosity, diffusion, and thermal conductivity

Exact state-to-state quantum dynamics of the F+HD→HF(v′ = 2)+D reaction on model potential energy surfaces

Dario De Fazio, Vincenzo Aquilanti, Simonetta Cavalli, Antonio Aguilar, and Josep M. Lucas

J. Chem. Phys. 129, 064303 (2008); http://dx.doi.org/10.1063/1.2964103 (8 pages) | Cited 10 times

Online Publication Date: 11 August 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
In this paper, we present the results of a theoretical investigation on the dynamics of the title reaction at collision energies below 1.2 kcal/mol using rigorous quantum reactive scattering calculations. Vibrationally resolved integral and differential cross sections, as well as product rotational distributions, have been calculated using two electronically adiabatic potential energy surfaces, developed by us on the basis of semiempirical modifications of the entrance channel. In particular, we focus our attention on the role of the exothermicity and of the exit channel region of the interaction on the experimental observables. From the comparison between the theoretical results, insight about the main mechanisms governing the reaction is extracted, especially regarding the bimodal structure of the HF(v = 2) nascent rotational state distributions. A good overall agreement with molecular beam scattering experiments has been obtained.
Show PACS
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.20.Kh Potential energy surfaces for chemical reactions
34.20.Gj Intermolecular and atom-molecule potentials and forces
33.15.Mt Rotation, vibration, and vibration-rotation constants

A simulation of the photoelectron spectrum of pyrazolide

Michael S. Schuurman and David R. Yarkony

J. Chem. Phys. 129, 064304 (2008); http://dx.doi.org/10.1063/1.2961042 (14 pages) | Cited 8 times

Online Publication Date: 11 August 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Building on previous theoretical and spectroscopic studies of the pyrazolyl radical, a new three-state quasidiabatic Hamiltonian is reported which reproduces not only the equilibrium geometries and harmonic frequencies of the nominal math 2A2 state and low-lying math 2B1 excited state, but also the minimum energy points on the lowest two-state (math 2A2,math 2B1) and three-state (math 2A2,math 2B1,math 2B2) seams of conical intersection. The three-state Hamiltonian includes all terms through second order in both the diagonal and off-diagonal blocks. Its construction is accomplished in two steps. First, a nascent Hamiltonian, centered at the lowest energy two-state conical intersection, is determined using ab initio gradients and derivative couplings. Then, the nascent Hamiltonian is improved by optimizing selected contributions to the second-order coefficients to better reproduce relevant minima and harmonic frequencies. This Hamiltonian is then expressed in a basis tailored to describe the neutral states of interest under the multimode vibronic coupling approximation. The vibronic Hamiltonian is diagonalized to obtain negative ion photoelectron spectra for pyrazolide-h3 and the completely deuterated analog pyrazolide-d3. The resultant spectra, determined employing vibronic Hamiltonians as large as 500 million terms, compare favorably to recent theoretical and spectroscopic results for pyrazolyl-d3 and to spectroscopic results for pyrazolyl-h3, for which no reliable simulations had been available.
Show PACS
33.60.+q Photoelectron spectra
31.15.A- Ab initio calculations
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions

Argon cluster-mediated isolation and vibrational spectra of peroxy and nominally D3h isomers of CO3− and NO3−

Rachael A. Relph, Joseph C. Bopp, Mark A. Johnson, and A. A. Viggiano

J. Chem. Phys. 129, 064305 (2008); http://dx.doi.org/10.1063/1.2958223 (6 pages) | Cited 1 time

Online Publication Date: 11 August 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Vibrational predissociation spectra are reported for two isomeric forms of the gas-phase ions, CO3− and NO3−. The peroxy forms, (OOCO− and OONO−) were isolated using an Ar-mediated synthetic scheme involving exchange of CO and NO for the more weakly bound Ar ligands in O2−⋅Arm clusters, while the forms based on a central heteroatom (CO3− and NO3−) were generated by electron impact on CO2 and HNO3 vapor. The simple two-band spectrum of OOCO− indicates that it is best described as the O2−⋅CO ion-molecule complex, whereas the covalently bound CO3− form yields a much more complicated vibrational spectrum with bands extending out to 4000 cm−1. In contrast, the NO3− ion yields a simple spectrum with only one transition as expected for the antisymmetric NO stretching fundamental of a species with D3h structure. The spectrum of the peroxynitrite isomer, OONO−, displays intermediate complexity that can be largely understood in the context of fundamentals associated with its cis and trans structures previously characterized in an Ar matrix.
Show PACS
33.20.Tp Vibrational analysis
33.80.Gj Diffuse spectra; predissociation, photodissociation
34.80.Ht Dissociation and dissociative attachment
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)

Theoretical determination of rate constants for vibrational relaxation and reaction of OH(X 2Π,v = 1) with O(3P) atoms

Jacek A. Kłos, François Lique, Millard H. Alexander, and Paul J. Dagdigian

J. Chem. Phys. 129, 064306 (2008); http://dx.doi.org/10.1063/1.2957901 (10 pages) | Cited 8 times

Online Publication Date: 12 August 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Collisions of the vibrationally excited OH(v = 1) molecule with atomic oxygen are investigated theoretically using a coupled-states, statistical capture (CS-ST) model. Vibrational relaxation can occur by inelastic scattering, and the vibrationally excited molecule can also be removed by reaction to form O2 in both the ground (X 3Σg−) and first excited (a 1Δg) state. In the former case, reaction occurs on the lowest potential energy surface of 2A″ symmetry, and, in the latter case, by reaction on the lowest potential energy surface of 2A′ symmetry. We report new ab initio potential energy surfaces for both these states in the product and reactant regions necessary for application of the coupled-states, statistical method. Comparison with exact, reactive scattering calculations within the J-shifting approximation indicate that the CS-ST rate constants for removal of OH(v = 1) can be expected to be reasonably accurate. Our calculated rate constants at 300 K agree well with the experimental results of Khachatrian and Dagdigian [Chem. Phys. Lett. 415, 1 (2005)] . Reaction to yield O2 (X 3Σg−) is the dominant removal pathway. At subthermal temperatures, the rate constants for the various vibrational quenching processes all increase down to T ≅ 60 K and then decrease at lower temperature.
Show PACS
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.20.Kh Potential energy surfaces for chemical reactions
82.20.Pm Rate constants, reaction cross sections, and activation energies
Page 1 of 3 Pages Next Page | Jump to Page
Close

Google Calendar

ADVERTISEMENT

Your Recent History Recent History Help

Recently Viewed

  1. Effects of interaction range and compressibility on the microphase separation of diblock copolymers: Mean-field analysis
  2. Quantum mechanical methods applied to excitation energy transfer: A comparative analysis on excitation energies and electronic couplings
  3. A statistical analysis of the precision of reweighting-based simulations
  4. Multifunctional metal-doped carbon nanocapsules
  5. Erratum: “Comparison of efficiency and bias of free energies computed by exponential averaging, the Bennett acceptance ratio, and thermodynamic integration” [ J. Chem. Phys. 122, 144107 (2005) ]
Go to AIP Home
Copyright © American Institute of Physics
close