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 2011

Volume 135, Issue 4, Articles (04xxxx)

Issue Cover Spotlight Figure

J. Chem. Phys. 135, 044201 (2011); http://dx.doi.org/10.1063/1.3607236 (12 pages)

Jahan M. Dawlaty, Doran I. G. Bennett, Vanessa M. Huxter, and Graham R. Fleming
Enlarge Image | Read More
Page 1 of 4 Pages Next Page | Jump to Page
back to top
RSS Feeds
FREE

Communication: The formation of helium cluster cations following the ionization of helium nanodroplets: Influence of droplet size and dopant

Benjamin Shepperson, Jun Liu, Andrew M. Ellis, and Shengfu Yang

J. Chem. Phys. 135, 041101 (2011); http://dx.doi.org/10.1063/1.3622764 (4 pages)

Online Publication Date: 27 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The Hen+/He2+ (n ≥ 3) signal ratios in the mass spectra derived from electron impact ionization of pure helium nanodroplets are shown to increase with droplet size, reaching an asymptotic limit at an average droplet size of approximately 50 000 helium atoms. This is explained in terms of a charge hopping model, where on average the positive charge is able to penetrate more deeply into the liquid helium as the droplet size increases. The deeper the point where the charge localizes to form He2+, the greater the likelihood of collisions with the surrounding helium as the ion begins to leave the droplet, thus increasing the probability that helium will be ejected in the form of Hen+ (n ≥ 3) cluster ions rather than He2+. The addition of a dopant alters the Hen+/He2+ ratio for small helium droplets, an observation attributed to the potential energy gradient created by the cation-dopant interaction and its effect in drawing the positive charge towards the dopant in the interior of the droplet.
Show PACS
36.40.Wa Charged clusters
33.15.Ta Mass spectra
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions
34.80.Dp Atomic excitation and ionization
36.40.Mr Spectroscopy and geometrical structure of clusters
back to top
RSS Feeds
back to top Theoretical Methods and Algorithms

Quasi-degenerate second-order perturbation theory for occupation restricted multiple active space self-consistent field reference functions

Luke Roskop and Mark S. Gordon

J. Chem. Phys. 135, 044101 (2011); http://dx.doi.org/10.1063/1.3609756 (11 pages)

Online Publication Date: 22 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A multi-configuration quasi-degenerate second-order perturbation method based on the occupation restricted multiple active space (ORMAS-PT/ORMAS) reference wavefunction is presented. ORMAS gives one the ability to approximate a complete active space self-consistent field (CASSCF) wavefunction using only a subset of the configurations from the CASSCF space. The essential idea behind ORMAS-PT is to use the multi-reference Møller-Plesset formalism to correct the ORMAS reference energy. A computational scheme employing direct CI methodology is presented. Several tests are presented to demonstrate the performance of the ORMAS-PT method.
Show PACS
31.15.xr Self-consistent-field methods
31.15.am Relativistic configuration interaction (CI) and many-body perturbation calculations
31.15.xp Perturbation theory

On the effectiveness of CCSD(T) complete basis set extrapolations for atomization energies

David Feller, Kirk A. Peterson, and J. Grant Hill

J. Chem. Phys. 135, 044102 (2011); http://dx.doi.org/10.1063/1.3613639 (18 pages) | Cited 5 times

Online Publication Date: 22 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The leading cause of error in standard coupled cluster theory calculations of thermodynamic properties such as atomization energies and heats of formation originates with the truncation of the one-particle basis set expansion. Unfortunately, the use of finite basis sets is currently a computational necessity. Even with basis sets of quadruple zeta quality, errors can easily exceed 8 kcal/mol in small molecules, rendering the results of little practical use. Attempts to address this serious problem have led to a wide variety of proposals for simple complete basis set extrapolation formulas that exploit the regularity in the correlation consistent sequence of basis sets. This study explores the effectiveness of six formulas for reproducing the complete basis set limit. The W4 approach was also examined, although in lesser detail. Reference atomization energies were obtained from standard coupled-cluster singles, doubles, and perturbative triples (CCSD(T)) calculations involving basis sets of 6ζ or better quality for a collection of 141 molecules. In addition, a subset of 51 atomization energies was treated with explicitly correlated CCSD(T)-F12b calculations and very large basis sets. Of the formulas considered, all proved reliable at reducing the one-particle expansion error. Even the least effective formulas cut the error in the raw values by more than half, a feat requiring a much larger basis set without the aid of extrapolation. The most effective formulas cut the mean absolute deviation by a further factor of two. Careful examination of the complete body of statistics failed to reveal a single choice that out performed the others for all basis set combinations and all classes of molecules.
Show PACS
31.15.bw Coupled-cluster theory
33.15.Fm Bond strengths, dissociation energies
82.60.Cx Enthalpies of combustion, reaction, and formation

Electronic properties of metal-arene functionalized graphene

Paul Plachinda, David R. Evans, and Raj Solanki

J. Chem. Phys. 135, 044103 (2011); http://dx.doi.org/10.1063/1.3613649 (9 pages)

Online Publication Date: 22 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We have employed first-principles density-functional calculations to study the electronic characteristics of covalently functionalized graphene by metal-bis-arene chemistry. It is shown that functionalization with M-bis-arene (M = Ti, V, Cr, Mn, Fe) molecules leads to an opening in the bandgap of graphene (up to 0.81 eV for the Cr derivative), and as a result, transforms it from a semimetal to a semiconductor. The bandgap induced by attachment of a metal atom topped by a benzene ring is attributed to modification of π-conjugation and depends on the concentration of functionalizing molecules. This approach offers a means of tailoring the band structure of graphene and potentially its applications for future electronic devices.
Show PACS
71.20.Tx Fullerenes and related materials; intercalation compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.30.+h Metal-insulator transitions and other electronic transitions

Multicomponent diffusion in nanosystems

Umberto Marini Bettolo Marconi and Simone Melchionna

J. Chem. Phys. 135, 044104 (2011); http://dx.doi.org/10.1063/1.3608416 (11 pages)

Online Publication Date: 22 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We present the detailed analysis of the diffusive transport of spatially inhomogeneous fluid mixtures and the interplay between structural and dynamical properties varying on the atomic scale. The present treatment is based on different areas of liquid state theory, namely, kinetic and density functional theory and their implementation as an effective numerical method via the lattice Boltzmann approach. By combining the first two methods, it is possible to obtain a closed set of kinetic equations for the singlet phase space distribution functions of each species. The interactions among particles are considered within a self-consistent approximation and the resulting effective molecular fields are analyzed. We focus on multispecies diffusion in systems with short-range hard-core repulsion between particles of unequal sizes and weak attractive long-range interactions. As a result, the attractive part of the potential does not contribute explicitly to viscosity but to diffusivity and the thermodynamic properties. Finally, we obtain a practical scheme to solve the kinetic equations by employing a discretization procedure derived from the lattice Boltzmann approach. Within this framework, we present numerical data concerning the mutual diffusion properties both in the case of a quiescent bulk fluid and shear flow inducing Taylor dispersion.
Show PACS
66.10.C- Diffusion and thermal diffusion
64.75.Ef Mixing
65.20.-w Thermal properties of liquids
66.20.-d Viscosity of liquids; diffusive momentum transport
82.70.-y Disperse systems; complex fluids
02.60.-x Numerical approximation and analysis

Auxiliary basis sets for density fitting second-order Møller-Plesset perturbation theory: Correlation consistent basis sets for the 5d elements Hf-Pt

J. Grant Hill

J. Chem. Phys. 135, 044105 (2011); http://dx.doi.org/10.1063/1.3615062 (4 pages)

Online Publication Date: 22 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Auxiliary basis sets specifically matched to the correlation consistent cc-pVnZ-PP, cc-pwCVnZ-PP, aug-cc-pVnZ-PP, and aug-cc-pwCVnZ-PP orbital basis sets (used in conjunction with pseudopotentials) for the 5d transition metal elements Hf-Pt have been optimized for use in density fitting second-order Møller-Plesset perturbation theory and other correlated ab initio methods. Calculations of the second-order Møller-Plesset perturbation theory correlation energy, for a test set of small to medium sized molecules, indicate that the density fitting error when utilizing these sets is negligible at three to four orders of magnitude smaller than the orbital basis set incompleteness error.
Show PACS
31.15.xp Perturbation theory
31.15.A- Ab initio calculations

Functional derivative of the kinetic energy functional for spherically symmetric systems

Á. Nagy

J. Chem. Phys. 135, 044106 (2011); http://dx.doi.org/10.1063/1.3607313 (5 pages)

Online Publication Date: 25 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Ensemble non-interacting kinetic energy functional is constructed for spherically symmetric systems. The differential virial theorem is derived for the ensemble. A first-order differential equation for the functional derivative of the ensemble non-interacting kinetic energy functional and the ensemble Pauli potential is presented. This equation can be solved and a special case of the solution provides the original non-interacting kinetic energy of the density functional theory.
Show PACS
31.15.E- Density-functional theory

On the coupling between slow diffusion transport and barrier crossing in nucleation

Baron Peters

J. Chem. Phys. 135, 044107 (2011); http://dx.doi.org/10.1063/1.3613674 (10 pages) | Cited 1 time

Online Publication Date: 25 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We model the coupling between slow diffusion transport and nucleation using the diffusion equation, an Ostwald-Freundlich boundary condition, and a mass balance linking nucleus size to flux across the nucleus-solution interface. The model retains some characteristics of the classical nucleation theory because of the common theoretical foundations behind classical nucleation theory and the Ostwald-Freundlich equation. For example, the classically critical-sized nucleus in the uniform supersaturated concentration field is an unstable equilibrium point. However, the model also shows that certain types of concentration profiles can drive a classically pre-critical nucleus over the nucleation barrier. We identify the separatrix as a function of both nucleus size and characteristics of the local concentration field. Our analysis may be useful for understanding the effects of local concentration fluctuations and especially for understanding the role of dense precursor particles in driving two-step nucleation processes. Our analysis may also provide a starting point for further statistical field theory analyses of local concentration fluctuations and their effects on nucleation rates.
Show PACS
64.60.qe General theory and computer simulations of nucleation
66.10.cd Thermal diffusion and diffusive energy transport
64.70.dg Crystallization of specific substances

Theoretical investigation of resonance Raman scattering of dye molecules absorbed on semiconductor surfaces

Yi Zhao and WanZhen Liang

J. Chem. Phys. 135, 044108 (2011); http://dx.doi.org/10.1063/1.3615057 (8 pages) | Cited 1 time

Online Publication Date: 25 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A method in time domain is proposed to investigate resonance Raman spectra of absorbed molecules on semiconductor surfaces. The charge transfer at the molecule-surface interface is incorporated with the use of an Anderson-Newns type Hamiltonian, where the surface continuum state is dealt with an expansion of Legendre polynomials for fast numerical convergence. From a model test, it is found that the intensities of Raman modes in the sole molecule generally decrease as the molecule-surface interaction is switched on, except that the energy gaps between the molecular excited state and the bottom of the band are at special values. New Raman peaks which are not observed in the sole molecule, however, appear and are greatly enhanced. The enhancement depends on the electronic coupling and the energy gap. It is also highly sensitive to the mode-specific reorganization energy in the charge transfer state, and a thousand times enhancement can be obtained at a certain reorganization energy. The corresponding electron dynamics is revealed by the population decay from the absorbed molecule.
Show PACS
78.30.-j Infrared and Raman spectra
02.10.De Algebraic structures and number theory
71.20.Rv Polymers and organic compounds

Introduction of the Floquet-Magnus expansion in solid-state nuclear magnetic resonance spectroscopy

Eugène S. Mananga and Thibault Charpentier

J. Chem. Phys. 135, 044109 (2011); http://dx.doi.org/10.1063/1.3610943 (11 pages)

Online Publication Date: 25 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
In this article, we present an alternative expansion scheme called Floquet-Magnus expansion (FME) used to solve a time-dependent linear differential equation which is a central problem in quantum physics in general and solid-state nuclear magnetic resonance (NMR) in particular. The commonly used methods to treat theoretical problems in solid-state NMR are the average Hamiltonian theory (AHT) and the Floquet theory (FT), which have been successful for designing sophisticated pulse sequences and understanding of different experiments. To the best of our knowledge, this is the first report of the FME scheme in the context of solid state NMR and we compare this approach with other series expansions. We present a modified FME scheme highlighting the importance of the (time-periodic) boundary conditions. This modified scheme greatly simplifies the calculation of higher order terms and shown to be equivalent to the Floquet theory (single or multimode time-dependence) but allows one to derive the effective Hamiltonian in the Hilbert space. Basic applications of the FME scheme are described and compared to previous treatments based on AHT, FT, and static perturbation theory. We discuss also the convergence aspects of the three schemes (AHT, FT, and FME) and present the relevant references.
Show PACS
76.60.-k Nuclear magnetic resonance and relaxation
02.30.-f Function theory, analysis

Analytic energy gradient for second-order Møller-Plesset perturbation theory based on the fragment molecular orbital method

Takeshi Nagata, Dmitri G. Fedorov, Kazuya Ishimura, and Kazuo Kitaura

J. Chem. Phys. 135, 044110 (2011); http://dx.doi.org/10.1063/1.3611020 (15 pages)

Online Publication Date: 25 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The first derivative of the total energy with respect to nuclear coordinates (the energy gradient) in the fragment molecular orbital (FMO) method is applied to second order Møller-Plesset perturbation theory (MP2), resulting in the analytic derivative of the correlation energy in the external self-consistent electrostatic field. The completely analytic energy gradient equations are formulated at the FMO-MP2 level. Both for molecular clusters (H2O)64 and a system with fragmentation across covalent bonds, a capped alanine decamer, the analytic FMO-MP2 energy gradients with the electrostatic dimer approximation are shown to be complete and accurate by comparing them with the corresponding numeric gradients. The developed gradient is parallelized with the parallel efficiency of about 97% on 32 Pentium4 nodes connected by Gigabit Ethernet.
Show PACS
36.40.Cg Electronic and magnetic properties of clusters
31.15.xp Perturbation theory
33.15.Fm Bond strengths, dissociation energies
31.15.bw Coupled-cluster theory

Fluctuating hydrodynamics for multiscale simulation of inhomogeneous fluids: Mapping all-atom molecular dynamics to capillary waves

Barry Z. Shang, Nikolaos K. Voulgarakis, and Jhih-Wei Chu

J. Chem. Phys. 135, 044111 (2011); http://dx.doi.org/10.1063/1.3615719 (12 pages)

Online Publication Date: 26 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We introduce a multiscale framework to simulate inhomogeneous fluids by coarse-graining an all-atom molecular dynamics (MD) trajectory onto sequential snapshots of hydrodynamic fields. We show that the field representation of an atomistic trajectory is quantitatively described by a dynamic field-theoretic model that couples hydrodynamic fluctuations with a Ginzburg-Landau free energy. For liquid-vapor interfaces of argon and water, the parameters of the field model can be adjusted to reproduce the bulk compressibility and surface tension calculated from the positions and forces of atoms in an MD simulation. These optimized parameters also enable the field model to reproduce the static and dynamic capillary wave spectra calculated from atomistic coordinates at the liquid-vapor interface. In addition, we show that a density-dependent gradient coefficient in the Ginzburg-Landau free energy enables bulk and interfacial fluctuations to be controlled separately. For water, this additional degree of freedom is necessary to capture both the bulk compressibility and surface tension emergent from the atomistic trajectory. The proposed multiscale framework illustrates that bottom-up coarse-graining and top-down phenomenology can be integrated with quantitative consistency to simulate the interfacial fluctuations in nanoscale transport processes.
Show PACS
61.20.Ja Computer simulation of liquid structure
47.35.Pq Capillary waves
68.03.Kn Dynamics (capillary waves)
68.03.Cd Surface tension and related phenomena
65.20.Jk Studies of thermodynamic properties of specific liquids
47.85.Dh Hydrodynamics, hydraulics, hydrostatics

Particle-based multiscale coarse graining with density-dependent potentials: Application to molecular crystals (hexahydro-1,3,5-trinitro-s-triazine)

Sergei Izvekov, Peter W. Chung, and Betsy M. Rice

J. Chem. Phys. 135, 044112 (2011); http://dx.doi.org/10.1063/1.3607603 (17 pages)

Online Publication Date: 27 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We describe the development of isotropic particle-based coarse-grain models for crystalline hexahydro-1,3,5-trinitro-s-triazine (RDX). The coarse graining employs the recently proposed multiscale coarse-graining (MS-CG) method, which is a particle-based force-matching approach for deriving free-energy effective interaction potentials. Though one-site and four-site coarse-grain (CG) models were parameterized from atomistic simulations of non-ordered (molten and ambient temperature amorphous) systems, the focus of the paper is a detailed study of the one-site model with a brief recourse to the four-site model. To improve the ability of the one-site model to be applied to crystalline phases at various pressures, it was found necessary to include explicit dependence on a particle density, and a new theory of local density-dependent MS-CG potentials is subsequently presented. The density-dependency is implemented through interpolation of MS-CG force fields derived at a preselected set of reference densities. The computationally economical procedure for obtaining the reference force fields starting from the interaction at ambient density is also described. The one-site MS-CG model adequately describes the atomistic lattice structure of α-RDX at ambient and high pressures, elastic and vibrational properties, pressure-volume curve up to P = 10 GPa, and the melting temperature. In the molten state, the model reproduces the correct pair structure at different pressures as well as higher order correlations. The potential of the MS-CG model is further evaluated in simulations of shocked crystalline RDX
Show PACS
36.20.Ng Vibrational and rotational structure, infrared and Raman spectra
65.40.G- Other thermodynamical quantities
02.60.Ed Interpolation; curve fitting
33.20.Tp Vibrational analysis

Approximate variational coupled cluster theory

James B. Robinson and Peter J. Knowles

J. Chem. Phys. 135, 044113 (2011); http://dx.doi.org/10.1063/1.3615060 (9 pages) | Cited 1 time

Online Publication Date: 27 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We show that it is possible to construct an accurate approximation to the variational coupled cluster method, limited to double substitutions, from the minimization of a functional that is rigorously extensive, exact for isolated two-electron subsystems and invariant to transformations of the underlying orbital basis. This approximate variational coupled cluster theory is a modification and enhancement of our earlier linked pair functional theory. It is first motivated by the constraint that the inverse square root of the matrix that transforms the cluster amplitudes must exist. Low-order corrections are then included to enhance the accuracy of the approximation of variational coupled cluster, while ensuring that the computational complexity of the method never exceeds that of the standard traditional coupled cluster method. The effects of single excitations are included by energy minimization with respect to the orbitals defining the reference wavefunction. The resulting quantum chemical method is demonstrated to be a robust approach to the calculation of molecular electronic structure and performs well when static correlation effects are strong.
Show PACS
31.15.bw Coupled-cluster theory
31.15.xt Variational techniques

Diabatic couplings for charge recombination via Boys localization and spin-flip configuration interaction singles

Ethan Alguire and Joseph E. Subotnik

J. Chem. Phys. 135, 044114 (2011); http://dx.doi.org/10.1063/1.3615493 (8 pages)

Online Publication Date: 27 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We describe a straightforward technique for obtaining diabatic couplings applicable to charge transfer from or charge recombination to the electronic ground state. Our method is nearly black box, requiring minimal chemical intuition from the user, and merges two well-established approaches in electronic structure theory: first, smooth and balanced adiabatic states are generated using spin-flip-configuration interaction singles (SF-CIS) based on a triplet HF state; second, Boys localization is applied to rotate all adiabatic states into charge-localized diabatic states. The method is computationally inexpensive, scaling only with the cost of CIS, and does not require a choice of active space, which is usually required for such intrinsically multiconfigurational problems. Molecular LiF in vacuum and LiF solvated by a single water molecule are examined as model systems. We find nearly smooth diabatic potential energy surfaces and couplings and we find that the Condon approximation is obeyed approximately for this model problem.
Show PACS
31.15.V- Electron correlation calculations for atoms, ions and molecules
31.50.Bc Potential energy surfaces for ground electronic states
31.50.Df Potential energy surfaces for excited electronic states
34.70.+e Charge transfer

Empirical valence bond models for reactive potential energy surfaces: A parallel multilevel genetic program approach

Michael A. Bellucci and David F. Coker

J. Chem. Phys. 135, 044115 (2011); http://dx.doi.org/10.1063/1.3610907 (17 pages) | Cited 1 time

Online Publication Date: 27 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We describe a new method for constructing empirical valence bond potential energy surfaces using a parallel multilevel genetic program (PMLGP). Genetic programs can be used to perform an efficient search through function space and parameter space to find the best functions and sets of parameters that fit energies obtained by ab initio electronic structure calculations. Building on the traditional genetic program approach, the PMLGP utilizes a hierarchy of genetic programming on two different levels. The lower level genetic programs are used to optimize coevolving populations in parallel while the higher level genetic program (HLGP) is used to optimize the genetic operator probabilities of the lower level genetic programs. The HLGP allows the algorithm to dynamically learn the mutation or combination of mutations that most effectively increase the fitness of the populations, causing a significant increase in the algorithm's accuracy and efficiency. The algorithm's accuracy and efficiency is tested against a standard parallel genetic program with a variety of one-dimensional test cases. Subsequently, the PMLGP is utilized to obtain an accurate empirical valence bond model for proton transfer in 3-hydroxy-gamma-pyrone in gas phase and protic solvent.
Show PACS
82.20.Kh Potential energy surfaces for chemical reactions
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
02.60.Pn Numerical optimization
82.20.Wt Computational modeling; simulation

A new perspective on transition states: χ1 separatrix

Paul J. Ledbetter and Cecilia Clementi

J. Chem. Phys. 135, 044116 (2011); http://dx.doi.org/10.1063/1.3610957 (13 pages)

Online Publication Date: 27 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We present a new definition of the transition state for chemical reactions, named the χ1 separatrix. In contrast to previous transition state definitions which depend on the choice of reaction coordinates, the χ1 separatrix is defined by choosing a time scale for observation and is connected to exact rate constants in the high friction limit. We demonstrate that this separatrix appears in the isomerization of alanine dipeptide as a stationary population in quasi-equilibrium, without assuming a particular coordinate system or reactant and product surfaces.
Show PACS
82.20.Db Transition state theory and statistical theories of rate constants
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.30.Qt Isomerization and rearrangement

GVVPT2 energy gradient using a Lagrangian formulation

Daniel Theis, Yuriy G. Khait, and Mark R. Hoffmann

J. Chem. Phys. 135, 044117 (2011); http://dx.doi.org/10.1063/1.3611049 (14 pages)

Online Publication Date: 27 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A Lagrangian based approach was used to obtain analytic formulas for GVVPT2 energy nuclear gradients. The formalism can use either complete or incomplete model (or reference) spaces, and is limited, in this regard, only by the capabilities of the MCSCF program. An efficient means of evaluating the gradient equations is described. Demonstrative calculations were performed and compared with finite difference calculations on several molecules and show that the GVVPT2 gradients are accurate. Of particular interest, the suggested formalism can straightforwardly use state-averaged MCSCF descriptions of the reference space in which the states have arbitrary weights. This capability is demonstrated by some calculations on the ground and first excited singlet states of LiH, including calculations near an avoided crossing. The accuracy and usefulness of the GVVPT2 method and its gradient are highlighted by comparing the geometry of the near-C2v minimum on the conical intersection seam between the 1 1A1 and 2 1A1 surfaces of O3 with values that were calculated at the multireference configuration interaction, including single and double excitations (MRCISD), level of theory.
Show PACS
31.15.xr Self-consistent-field methods
31.50.Df Potential energy surfaces for excited electronic states

Density functional study of multiplicity-changing valence and Rydberg excitations of p-block elements: Delta self-consistent field, collinear spin-flip time-dependent density functional theory (DFT), and conventional time-dependent DFT

Ke Yang, Roberto Peverati, Donald G. Truhlar, and Rosendo Valero

J. Chem. Phys. 135, 044118 (2011); http://dx.doi.org/10.1063/1.3607312 (22 pages) | Cited 2 times

Online Publication Date: 28 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A database containing 17 multiplicity-changing valence and Rydberg excitation energies of p-block elements is used to test the performance of density functional theory (DFT) with approximate density functionals for calculating relative energies of spin states. We consider only systems where both the low-spin and high-spin state are well described by a single Slater determinant, thereby avoiding complications due to broken-symmetry solutions. Because the excitations studied involve a spin change, they require a balanced treatment of exchange and correlation, thus providing a hard test for approximate density functionals. We test three formalisms for predicting the multiplicity-changing transition energies. First is the ΔSCF method; we also test time-dependent density functional theory (TDDFT), both in its conventional form starting from the low-spin state and in its collinear spin-flip form starting from the high-spin state. Very diffuse basis functions are needed to give a qualitatively correct description of the Rydberg excitations. The scalar relativistic effect needs to be considered when quantitative results are desired, and we include it in the comparisons. With the ΔSCF method, most of the tested functionals give mean unsigned errors (MUEs) larger than 6 kcal/mol for valence excitations and MUEs larger than 3 kcal/mol for Rydberg excitations, but the performance for the Rydberg states is much better than can be obtained with time-dependent DFT. It is surprising to see that the long-range corrected functionals, which have 100% Hartree–Fock exchange at large inter-electronic distance, do not improve the performance for Rydberg excitations. Among all tested density functionals, ΔSCF calculations with the O3LYP, M08-HX, and OLYP functionals give the best overall performance for both valence and Rydberg excitations, with MUEs of 2.1, 2.6, and 2.7 kcal/mol, respectively. This is very encouraging since the MUE of the CCSD(T) coupled cluster method with quintuple zeta basis sets is 2.0 kcal/mol; however, caution is advised since many popular density functionals give poor results, and there can be very significant differences between the ΔSCF predictions and those from TDDFT.
Show PACS
31.15.ee Time-dependent density functional theory
31.15.xr Self-consistent-field methods
31.30.J- Relativistic and quantum electrodynamic (QED) effects in atoms, molecules, and ions
31.15.bw Coupled-cluster theory

Seniority and orbital symmetry as tools for establishing a full configuration interaction hierarchy

Laimutis Bytautas, Thomas M. Henderson, Carlos A. Jiménez-Hoyos, Jason K. Ellis, and Gustavo E. Scuseria

J. Chem. Phys. 135, 044119 (2011); http://dx.doi.org/10.1063/1.3613706 (12 pages) | Cited 1 time

Online Publication Date: 28 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We explore the concept of seniority number (defined as the number of unpaired electrons in a determinant) when applied to the problem of electron correlation in atomic and molecular systems. Although seniority is a good quantum number only for certain model Hamiltonians (such as the pairing Hamiltonian), we show that it provides a useful partitioning of the electronic full configuration interaction (FCI) wave function into rapidly convergent Hilbert subspaces whose weight diminishes as its seniority number increases. The primary focus of this study is the adequate description of static correlation effects. The examples considered are the ground states of the helium, beryllium, and neon atoms, the symmetric dissociation of the N2 and CO2 molecules, as well as the symmetric dissociation of an H8 hydrogen chain. It is found that the symmetry constraints that are normally placed on the spatial orbitals greatly affect the convergence rate of the FCI expansion. The energy relevance of the seniority zero sector (determinants with all paired electrons) increases dramatically if orbitals of broken spatial symmetry (as those commonly used for Hubbard Hamiltonian studies) are allowed in the wave function construction.
Show PACS
31.15.V- Electron correlation calculations for atoms, ions and molecules

Correlated electron dynamics with time-dependent quantum Monte Carlo: Three-dimensional helium

Ivan P. Christov

J. Chem. Phys. 135, 044120 (2011); http://dx.doi.org/10.1063/1.3615061 (7 pages) | Cited 2 times

Online Publication Date: 28 July 2011

Full Text: Read Online (HTML) | Download PDF


See Also: Erratum

Show Abstract
Here the recently proposed time-dependent quantum Monte Carlo method is applied to three dimensional para- and ortho-helium atoms subjected to an external electromagnetic field with amplitude sufficient to cause significant ionization. By solving concurrently sets of up to 20 000 coupled 3D time-dependent Schrödinger equations for the guide waves and corresponding sets of first order equations of motion for the Monte Carlo walkers we obtain ground state energies in close agreement with the exact values. The combined use of spherical coordinates and B-splines along the radial coordinate proves to be especially accurate and efficient for such calculations. Our results for the dipole response and the ionization of an atom with un-correlated electrons are in good agreement with the predictions of the conventional time-dependent Hartree-Fock method while the calculations with correlated electrons show enhanced ionization that is due to the electron-electron repulsion.
Show PACS
31.15.-p Calculations and mathematical techniques in atomic and molecular physics
34.50.Fa Electronic excitation and ionization of atoms (including beam-foil excitation and ionization)
02.70.Ss Quantum Monte Carlo methods
03.65.Ge Solutions of wave equations: bound states

Multi-reference Fock space coupled-cluster method in the intermediate Hamiltonian formulation for potential energy surfaces

Monika Musiał and Rodney J. Bartlett

J. Chem. Phys. 135, 044121 (2011); http://dx.doi.org/10.1063/1.3615500 (8 pages) | Cited 2 times

Online Publication Date: 28 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The effective and intermediate Hamiltonian multi-reference coupled-cluster (CC) method with singles and doubles for the doubly ionized (0,2) sector of Fock space (FS) is formulated and implemented. The intermediate Hamiltonian realization of the (0,2) FS problem provides a robust computational scheme for solving the FS-CC equations free from the intruder state problem. By introducing an efficient factorization strategy, we obtain a very efficient tool that can be used for computing double ionization potentials but more significantly to describe multi-reference problems in CC theory, illustrated by twisted ethylene and the potential energy curve for F2. The latter separates smoothly to two F atoms, while the former avoids the cusp behavior at the 90° dihedral. We also explore the double ionization potentials for several small molecules, H2O, CO, C2H2, and C2H4.
Show PACS
31.15.bw Coupled-cluster theory
31.50.Bc Potential energy surfaces for ground electronic states
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy

Lagrangian formulation with dissipation of Born-Oppenheimer molecular dynamics using the density-functional tight-binding method

Guishan Zheng, Anders M. N. Niklasson, and Martin Karplus

J. Chem. Phys. 135, 044122 (2011); http://dx.doi.org/10.1063/1.3605303 (17 pages) | Cited 2 times

Online Publication Date: 28 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
An important element determining the time requirements of Born-Oppenheimer molecular dynamics (BOMD) is the convergence rate of the self-consistent solution of Roothaan equations (SCF). We show here that improved convergence and dynamics stability can be achieved by use of a Lagrangian formalism of BOMD with dissipation (DXL-BOMD). In the DXL-BOMD algorithm, an auxiliary electronic variable (e.g., the electron density or Fock matrix) is propagated and a dissipative force is added in the propagation to maintain the stability of the dynamics. Implementation of the approach in the self-consistent charge density functional tight-binding method makes possible simulations that are several hundred picoseconds in lengths, in contrast to earlier DFT-based BOMD calculations, which have been limited to tens of picoseconds or less. The increase in the simulation time results in a more meaningful evaluation of the DXL-BOMD method. A comparison is made of the number of iterations (and time) required for convergence of the SCF with DXL-BOMD and a standard method (starting with a zero charge guess for all atoms at each step), which gives accurate propagation with reasonable SCF convergence criteria. From tests using NVE simulations of C2F4 and 20 neutral amino acid molecules in the gas phase, it is found that DXL-BOMD can improve SCF convergence by up to a factor of two over the standard method. Corresponding results are obtained in simulations of 32 water molecules in a periodic box. Linear response theory is used to analyze the relationship between the energy drift and the correlation of geometry propagation errors.
Show PACS
31.15.E- Density-functional theory
31.15.xv Molecular dynamics and other numerical methods
31.15.xr Self-consistent-field methods
31.15.aq Strongly correlated electron systems: generalized tight-binding method

Development of a 3-body:many-body integrated fragmentation method for weakly bound clusters and application to water clusters (H2O)n = 3 − 10, 16, 17

Desiree M. Bates, Joshua R. Smith, Tomasz Janowski, and Gregory S. Tschumper

J. Chem. Phys. 135, 044123 (2011); http://dx.doi.org/10.1063/1.3609922 (8 pages) | Cited 1 time

Online Publication Date: 29 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A 3-body:many-body integrated quantum mechanical (QM) fragmentation method for non-covalent clusters is introduced within the ONIOM formalism. The technique captures all 1-, 2-, and 3-body interactions with a high-level electronic structure method, while a less demanding low-level method is employed to recover 4-body and higher-order interactions. When systematically applied to 40 low-lying (H2O)n isomers ranging in size from n = 3 to 10, the CCSD(T):MP2 3-body:many-body fragmentation scheme deviates from the full CCSD(T) interaction energy by no more than 0.07 kcal mol−1 (or <0.01 kcal mol−1 per water). The errors for this QM:QM method increase only slightly for various low-lying isomers of (H2O)16 and (H2O)17 (always within 0.13 kcal mol−1 of the recently reported canonical CCSD(T)/aug-cc-pVTZ energies). The 3-body:many-body CCSD(T):MP2 procedure is also very efficient because the CCSD(T) computations only need to be performed on subsets of the cluster containing 1, 2, or 3 monomers, which in the current context means the largest CCSD(T) calculations are for 3 water molecules, regardless of the cluster size.
Show PACS
36.40.Qv Stability and fragmentation of clusters
31.15.bw Coupled-cluster theory
31.15.xp Perturbation theory
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
36.40.Cg Electronic and magnetic properties of clusters
36.40.Mr Spectroscopy and geometrical structure of clusters

Effects of the dielectric discontinuity on the counterion distribution in a colloidal suspension

Alexandre P. dos Santos, Amin Bakhshandeh, and Yan Levin

J. Chem. Phys. 135, 044124 (2011); http://dx.doi.org/10.1063/1.3615940 (5 pages) | Cited 3 times

Online Publication Date: 29 July 2011

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We introduce a new method for simulating colloidal suspensions with spherical colloidal particles of dielectric constant different from the surrounding medium. The method uses an approximate calculation of the Green function to obtain the ion-ion interaction potential in the presence of a dielectric discontinuity at the surface of the colloidal particle. The method is very accurate and is orders of magnitude faster than the traditional approaches based on series expansions of the interaction potential.
Show PACS
82.70.Kj Emulsions and suspensions
82.70.Dd Colloids
77.22.Ch Permittivity (dielectric function)
Page 1 of 4 Pages Next Page | Jump to Page
Close

Google Calendar

ADVERTISEMENT

Your Recent History Recent History Help

Recently Viewed

  1. Note: Accurate ab initio predictions of ionization energies of propargyl and allyl radicals: Revisited
  2. Conformational fluctuations of a protein–DNA complex and the structure and ordering of water around it
  3. A two-dimensional-reference interaction site model theory for solvation structure near solid-liquid interface
  4. Thermal fluctuations in shape, thickness, and molecular orientation in lipid bilayers
  5. Accurate ab initio quartic force fields of cyclic and bent HC2N isomers
Go to AIP Home
Copyright © American Institute of Physics
close