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

You Tube Flickr Twitter iResearch App Facebook

BROWSE VOLUMES

Year Range: 
Search Issue | RSS Feeds RSS
Previous Issue

28 Dec 2009

Volume 131, Issue 24, Articles (24xxxx)

Issue Cover Spotlight Figure

J. Chem. Phys. 131, 244702 (2009); http://dx.doi.org/10.1063/1.3271910 (6 pages)

Irene Yeriskin and Michael Nolan
Enlarge Image | Read More
Page 1 of 4 Pages Next Page | Jump to Page
back to top
RSS Feeds
FREE

Correlation energy of two electrons in the high-density limit

Pierre-François Loos and Peter M. W. Gill

J. Chem. Phys. 131, 241101 (2009); http://dx.doi.org/10.1063/1.3275519 (4 pages) | Cited 13 times

Online Publication Date: 22 December 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We consider the high-density-limit correlation energy Ec in D ≥ 2 dimensions for the math ground states of three two-electron systems: helium (in which the electrons move in a Coulombic field), spherium (in which they move on the surface of a sphere), and hookium (in which they move in a quadratic potential). We find that the Ec values are strikingly similar, depending strongly on D but only weakly on the external potential. We conjecture that for large D, the limiting correlation energy Ec ∼ −δ2/8 in any confining external potential, where δ = 1/(D−1).
Show PACS
31.15.ve Electron correlation calculations for atoms and ions: ground state
FREE

Europium dimer: van der Waals molecule with extremely weak antiferromagnetic spin coupling

Alexei A. Buchachenko, Grzegorz Chałasiński, and Małgorzata M. Szczęśniak

J. Chem. Phys. 131, 241102 (2009); http://dx.doi.org/10.1063/1.3282332 (4 pages) | Cited 3 times

Online Publication Date: 29 December 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
High-level ab initio calculations reveal that the Eu2 dimer is a van der Waals molecule with extremely weak antiferromagnetic spin coupling. The Heisenberg spin-exchange model, validated by the multireference configuration interaction method, is used to construct the full set of model interaction potentials for the states with the total spin S ranging from 0 to 7 at the coupled cluster level of theory. This model establishes the singlet math state as the ground one of the dimer with the binding energy of 710 cm−1, the vibrational frequency of 23 cm−1 and the effective spin-coupling constant J estimated approximately −0.3 cm−1.
Show PACS
75.10.Jm Quantized spin models, including quantum spin frustration
75.50.Ee Antiferromagnetics
71.15.-m Methods of electronic structure calculations
71.20.Eh Rare earth metals and alloys
75.30.Et Exchange and superexchange interactions
FREE

Large enhancement of the vibration-rotation coupling of the ν1 and ν3 states of silane in helium droplets

Dmitry Skvortsov, Daniil Marinov, Boris G. Sartakov, and Andrey F. Vilesov

J. Chem. Phys. 131, 241103 (2009); http://dx.doi.org/10.1063/1.3282446 (4 pages) | Cited 1 time

Online Publication Date: 29 December 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Silane molecules have been embedded in helium droplets and studied via infrared laser depletion spectroscopy in the range of 2190 cm−1. We found that the R1 and Q2 lines of the ν3 band have satellites shifted by about 2.3 cm−1 towards low frequency and having similar intensity to the main lines. We assigned this perturbation in the spectrum to the coupling of the J = 2 levels in ν3 and close lying ν1 vibration states. The strength of the coupling is a factor of about 50 larger in He droplets than in free molecules and have the same selection rules implied by the tetrahedral symmetry of SiH4 molecules. The perturbation, which cannot be explained within the framework of a Hamiltonian of free molecules, is evidence of strong coupling of the molecule with some He excitations in the molecular vicinity.
Show PACS
33.20.Ea Infrared spectra
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.80.-b Photon interactions with molecules
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.70.Jg Line and band widths, shapes, and shifts
FREE

Thermally driven molecular linear motors: A molecular dynamics study

H. A. Zambrano, J. H. Walther, and R. L. Jaffe

J. Chem. Phys. 131, 241104 (2009); http://dx.doi.org/10.1063/1.3281642 (3 pages) | Cited 8 times

Online Publication Date: 29 December 2009

Full Text: Read Online (HTML) | Download PDF


See Also: Publisher's Note

Show Abstract
We conduct molecular dynamics simulations of a molecular linear motor consisting of coaxial carbon nanotubes with a long outer carbon nanotube confining and guiding the motion of an inner short, capsulelike nanotube. The simulations indicate that the motion of the capsule can be controlled by thermophoretic forces induced by thermal gradients. The simulations find large terminal velocities of 100–400 nm/ns for imposed thermal gradients in the range of 1–3 K/nm. Moreover, the results indicate that the thermophoretic force is velocity dependent and its magnitude decreases for increasing velocity.
Show PACS
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
84.50.+d Electric motors
31.15.xv Molecular dynamics and other numerical methods
61.43.Bn Structural modeling: serial-addition models, computer simulation
FREE

Merging bond-order potentials with charge equilibration

Paul T. Mikulski, M. Todd Knippenberg, and Judith A. Harrison

J. Chem. Phys. 131, 241105 (2009); http://dx.doi.org/10.1063/1.3271798 (4 pages) | Cited 7 times

Online Publication Date: 29 December 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A method is presented for extending any bond-order potential (BOP) to include charge transfer between atoms through a modification of the split-charge equilibration (SQE) formalism. Variable limits on the maximum allowed charge transfer between atomic pairs are defined by mapping bond order to an amount of shared charge in each bond. Charge transfer is interpreted as an asymmetry in how the shared charge is distributed between the atoms of the bond. Charge equilibration (QE) assesses the asymmetry of the shared charge, while the BOP converts this asymmetry to the actual amount of charge transferred. When applied to large molecules, this BOP/SQE method does not exhibit the unrealistic growth of charges that is often associated with QE models.
Show PACS
34.70.+e Charge transfer
33.15.Fm Bond strengths, dissociation energies
back to top
RSS Feeds
back to top Theoretical Methods and Algorithms

Derivation of dynamical density functional theory using the projection operator technique

Pep Español and Hartmut Löwen

J. Chem. Phys. 131, 244101 (2009); http://dx.doi.org/10.1063/1.3266943 (7 pages) | Cited 17 times

Online Publication Date: 22 December 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Density functional theory is a particular case of a general theory of conjugate variables that serves as the basis of the projection operator technique. By using this technique we derive a general dynamical version of density functional theory which involves a generalized diffusion tensor. The diffusion tensor is given by a Green–Kubo expression. For Brownian dynamics of dilute colloidal suspensions, the standard dynamical density functional theory is recovered.
Show PACS
61.20.Gy Theory and models of liquid structure
66.10.C- Diffusion and thermal diffusion
83.10.Mj Molecular dynamics, Brownian dynamics
82.70.Dd Colloids
82.70.Kj Emulsions and suspensions

An error-controlled fast multipole method

Holger Dachsel

J. Chem. Phys. 131, 244102 (2009); http://dx.doi.org/10.1063/1.3264952 (19 pages)

Online Publication Date: 22 December 2009

Full Text: Read Online (HTML) | Download PDF


See Also: Corrected Article

Show Abstract
We present a two-stage error estimation scheme for the fast multipole method (FMM). This scheme can be applied to any particle system. It incorporates homogeneous as well as inhomogeneous distributions. The FMM error as a consequence of the finite representation of the multipole expansions and the operator error is correlated with an absolute or relative user-requested energy threshold. Such a reliable error control is the basis for making reliable simulations in computational physics. Our FMM program on the basis of the two-stage error estimation scheme is available on request.
Show PACS
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions
34.10.+x General theories and models of atomic and molecular collisions and interactions (including statistical theories, transition state, stochastic and trajectory models, etc.)
52.40.Mj Particle beam interactions in plasmas

Competing nucleation pathways in a mixture of oppositely charged colloids: Out-of-equilibrium nucleation revisited

Baron Peters

J. Chem. Phys. 131, 244103 (2009); http://dx.doi.org/10.1063/1.3271024 (7 pages) | Cited 12 times

Online Publication Date: 22 December 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Recent simulations of crystal nucleation from a compressed liquid of oppositely charged colloids show that the natural Brownian dynamics results in nuclei of a charge-disordered FCC (DFCC) solid whereas artificially accelerated dynamics with charge swap moves result in charge-ordered nuclei of a CsCl phase. These results were interpreted as a breakdown of the quasiequilibrium assumption for precritical nuclei. We use structure-specific nucleus size coordinates for the CsCl and DFCC structures and equilibrium based sampling methods to understand the dynamical effects on structure selectivity in this system. Nonequilibrium effects observed in previous simulations emerge from a diffusion tensor that dramatically changes when charge swap moves are used. Without the charge swap moves diffusion is strongly anisotropic with very slow motion along the charge-ordered CsCl axis and faster motion along the DFCC axis. Kramers–Langer–Berezhkovskii–Szabo theory predicts that under the realistic dynamics, the diffusion anisotropy shifts the current toward the DFCC axis. The diffusion tensor also varies with location on the free energy landscape. A numerical calculation of the current field with a diffusion tensor that depends on the location in the free energy landscape exacerbates the extent to which the current is skewed toward DFCC structures. Our analysis confirms that quasiequilibrium theories based on equilibrium properties can explain the nonequilibrium behavior of this system. Our analysis also shows that using a structure-specific nucleus size coordinate for each possible nucleation product can provide mechanistic insight on selectivity and competition between nucleation pathways.
Show PACS
82.70.Dd Colloids
65.20.-w Thermal properties of liquids
61.20.-p Structure of liquids
66.10.C- Diffusion and thermal diffusion
62.10.+s Mechanical properties of liquids

Close packing density of polydisperse hard spheres

Robert S. Farr and Robert D. Groot

J. Chem. Phys. 131, 244104 (2009); http://dx.doi.org/10.1063/1.3276799 (7 pages) | Cited 31 times

Online Publication Date: 23 December 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The most efficient way to pack equally sized spheres isotropically in three dimensions is known as the random close packed state, which provides a starting point for many approximations in physics and engineering. However, the particle size distribution of a real granular material is never monodisperse. Here we present a simple but accurate approximation for the random close packing density of hard spheres of any size distribution based upon a mapping onto a one-dimensional problem. To test this theory we performed extensive simulations for mixtures of elastic spheres with hydrodynamic friction. The simulations show a general (but weak) dependence of the final (essentially hard sphere) packing density on fluid viscosity and on particle size but this can be eliminated by choosing a specific relation between mass and particle size, making the random close packed volume fraction well defined. Our theory agrees well with the simulations for bidisperse, tridisperse, and log-normal distributions and correctly reproduces the exact limits for large size ratios.
Show PACS
62.10.+s Mechanical properties of liquids
66.20.Cy Theory and modeling of viscosity and rheological properties, including computer simulation
61.20.Gy Theory and models of liquid structure
61.25.-f Studies of specific liquid structures

A theoretical study of the low-lying excited states of thieno[3,4-b]pyrazine

María D. Gómez-Jiménez, Rosendo Pou-Amérigo, and Enrique Ortí

J. Chem. Phys. 131, 244105 (2009); http://dx.doi.org/10.1063/1.3274816 (8 pages) | Cited 3 times

Online Publication Date: 28 December 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The low-lying electronic excited states of thieno[3,4-b]pyrazine have been studied using the multiconfigurational second-order perturbation CASPT2 theory with extended atomic natural orbital basis sets. The CASPT2 results allow for a full interpretation of the electronic absorption and emission spectra and provide valuable information for the rationalization of the experimental data. The nature, position, and intensity of the spectral bands have been analyzed in detail. A preliminary comparative study of the ground-state geometry of thieno[3,4-b]pyrazine has been performed at the coupled cluster single and doubles and density functional theory levels using a variety of correlation-consistent basis sets. Thieno[3,4-b]pyrazine exhibits a polyene-like structure in the ground state due to the bond localization in the pyrazine moiety. An aromatization of the pyrazine unit is predicted for the lowest-energy electronic excited states.
Show PACS
31.15.es Applications of density-functional theory (e.g., to electronic structure and stability; defect formation; dielectric properties, susceptibilities; viscoelastic coefficients; Rydberg transition frequencies)
31.15.bw Coupled-cluster theory
33.50.Dq Fluorescence and phosphorescence spectra

Higher-order symplectic integration in Born–Oppenheimer molecular dynamics

Anders Odell, Anna Delin, Börje Johansson, Nicolas Bock, Matt Challacombe, and Anders M. N. Niklasson

J. Chem. Phys. 131, 244106 (2009); http://dx.doi.org/10.1063/1.3268338 (10 pages) | Cited 8 times

Online Publication Date: 28 December 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The extended Lagrangian formulation of time-reversible Born–Oppenheimer molecular dynamics [ A. M. N. Niklasson, C. J. Tymczak, and M. Challacombe, Phys. Rev. Lett. 100, 123004 (2008) ; Phys. Rev. Lett. 97, 123001 (2006) ] enables the use of geometric integrators in the propagation of both the nuclear and the electronic degrees of freedom on the Born–Oppenheimer potential energy surface. Different symplectic integrators up to the sixth order have been adapted and optimized in the framework of ab initio self-consistent-field theory. It is shown how the accuracy can be significantly improved compared to a conventional Verlet integration at the same level of computational cost, in particular, for the case of very high accuracy requirements.
Show PACS
31.15.ae Electronic structure and bonding characteristics
31.15.xr Self-consistent-field methods
31.50.-x Potential energy surfaces

Coupling atomistic and continuum hydrodynamics through a mesoscopic model: Application to liquid water

Rafael Delgado-Buscalioni, Kurt Kremer, and Matej Praprotnik

J. Chem. Phys. 131, 244107 (2009); http://dx.doi.org/10.1063/1.3272265 (6 pages) | Cited 10 times

Online Publication Date: 28 December 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We have conducted a triple-scale simulation of liquid water by concurrently coupling atomistic, mesoscopic, and continuum models of the liquid. The presented triple-scale hydrodynamic solver for molecular liquids enables the insertion of large molecules into the atomistic domain through a mesoscopic region. We show that the triple-scale scheme is robust against the details of the mesoscopic model owing to the conservation of linear momentum by the adaptive resolution forces. Our multiscale approach is designed for molecular simulations of open domains with relatively large molecules, either in the grand canonical ensemble or under nonequilibrium conditions.
Show PACS
61.20.Ja Computer simulation of liquid structure
61.25.Em Molecular liquids

Accurate thermodynamics for short-ranged truncations of Coulomb interactions in site-site molecular models

Jocelyn M. Rodgers and John D. Weeks

J. Chem. Phys. 131, 244108 (2009); http://dx.doi.org/10.1063/1.3276729 (8 pages) | Cited 5 times

Online Publication Date: 29 December 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Coulomb interactions are present in a wide variety of all-atom force fields. Spherical truncations of these interactions permit fast simulations but are problematic due to their incorrect thermodynamics. Herein we demonstrate that simple analytical corrections for the thermodynamics of uniform truncated systems are possible. In particular, results for the simple point charge/extended (SPC/E) water model treated with spherically truncated Coulomb interactions suggested by local molecular field theory [ J. M. Rodgers and J. D. Weeks, Proc. Natl. Acad. Sci. U.S.A. 105, 19136 (2008) ] are presented. We extend the results developed by Chandler [ J. Chem. Phys. 65, 2925 (1976) ] so that we may treat the thermodynamics of mixtures of flexible charged and uncharged molecules simulated with spherical truncations. We show that the energy and pressure of spherically truncated bulk SPC/E water are easily corrected using exact second-moment-like conditions on long-ranged structure. Furthermore, applying the pressure correction as an external pressure removes the density errors observed by other research groups in NPT simulations of spherically truncated bulk species.
Show PACS
65.20.Jk Studies of thermodynamic properties of specific liquids
61.25.Em Molecular liquids

Role of ionization in orientation dependence of molecular high-order harmonic generation

Y. J. Chen and Bambi Hu

J. Chem. Phys. 131, 244109 (2009); http://dx.doi.org/10.1063/1.3275964 (5 pages) | Cited 1 time

Online Publication Date: 29 December 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We investigate the orientation dependence of high-order harmonic generation (HHG) from O2 and CO2 molecules using the strong-field approximation (SFA). Our simulations reveal the important modulation of the ionization to the HHG orientation dependence, especially at larger orientation angles. By virtue of a simplified model arising from the SFA, we show that this modulation can be read from the harmonic order where the HHG spectra at different orientation angles intersect. These results give suggestions on probing the molecular structure and dynamics using HHG.
Show PACS
33.80.Eh Autoionization, photoionization, and photodetachment
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
31.15.-p Calculations and mathematical techniques in atomic and molecular physics
33.15.Bh General molecular conformation and symmetry; stereochemistry

Conduction in graphenes

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

J. Chem. Phys. 131, 244110 (2009); http://dx.doi.org/10.1063/1.3272669 (8 pages) | Cited 9 times

Online Publication Date: 29 December 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
It is shown that, within the tight-binding approximation, Fermi-level ballistic conduction for a perimeter-connected graphene fragment follows a simple selection rule: the zero eigenvalues of the molecular graph and of its subgraph minus both contact vertices must be equal in number, as must those of the two subgraphs with single contact vertices deleted. In chemical terms, the new rule therefore involves counting nonbonding orbitals of four molecules. The rule is initially derived within the source and sink potential scattering framework, but has equivalent forms that unify the molecular-orbital and valence-bond approaches to conduction. It is shown that the new selection rule can be cast in terms of Kekulé counts, bond orders, and frontier-orbital coefficients. In particular, for a Kekulean graphene, conduction pathways are shown to be ranked in efficiency by a (nonmonotonic) function of Pauling bond order between the contact vertices. Frontier-orbital analysis of conduction approximates this function. For a monoradical graphene, the analogous function is shown to depend on Pauling spin densities at contact vertices.
Show PACS
73.63.-b Electronic transport in nanoscale materials and structures
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
73.23.Ad Ballistic transport
73.22.Pr Electronic structure of graphene
FREE

Critical points bifurcation analysis of high-ℓ bending dynamics in acetylene

Vivian Tyng and Michael E. Kellman

J. Chem. Phys. 131, 244111 (2009); http://dx.doi.org/10.1063/1.3264686 (11 pages) | Cited 3 times

Online Publication Date: 30 December 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The bending dynamics of acetylene with pure vibrational angular momentum excitation and quantum number ℓ ≠ 0 are analyzed through the method of critical points analysis, used previously [ V. Tyng and M. E. Kellman, J. Phys. Chem. B 110, 18859 (2006) ] for ℓ = 0 to find new anharmonic modes born in bifurcations of the low-energy normal modes. Critical points in the reduced phase space are computed for continuously varied bend polyad number Nb = n4+n5 as ℓ = ℓ4+ℓ5 is varied between 0 and 20. It is found that the local L, orthogonal O, precessional P, and counter-rotator CR families persist for all ℓ. In addition, for ℓ ≥ 8, there is a fifth family of critical points which, unlike the previous families, has no fixed relative phase (“off great circle” OGC). The concept of the minimum energy path in the polyad space is developed. With restriction to ℓ = 0 this is the local mode family L. This has an intuitive relation to the minimum energy path or reaction mode for acetylene-vinylidene isomerization. With ℓ ≥ 0 included as a polyad number, the ℓ = 0 minimum energy path forms a troughlike channel in the minimum energy surface in the polyad space, which consists of a complex mosaic of L, O, and OGC critical points. There is a division of the complete set of critical points into layers, the minimum energy surface forming the lowest.
Show PACS
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
33.15.Dj Interatomic distances and angles
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis
31.50.Df Potential energy surfaces for excited electronic states

Global phase diagrams for a compressible polymer-solvent system using the full Tompa model

Mustafa Gençaslan and Mustafa Keskin

J. Chem. Phys. 131, 244112 (2009); http://dx.doi.org/10.1063/1.3271832 (7 pages) | Cited 3 times

Online Publication Date: 30 December 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We present the global phase diagrams for a compressible polymer-solvent system at the mathematical double point and its environment by using the full Tompa model for varying numbers of segments in each polymer chain. A principal transition mechanism is a mathematical double point at which two critical lines meet and exchange branches. We present the critical lines in the density-density and the P, T planes in detail. The locations of all significant features of the phase diagrams are described and compared with Scott and van Konynenburg phase diagram classifications. We find the type II, type III or type IV phase diagram behaviors of the Scott and van Konynenburg classifications. It is also found that the critical lines and phase behavior are extremely sensitive to small modifications in the chain length parameter.
Show PACS
81.30.Dz Phase diagrams of other materials
61.25.he Polymer solutions

Four-component relativistic theory for nuclear magnetic shielding: Magnetically balanced gauge-including atomic orbitals

Lan Cheng, Yunlong Xiao, and Wenjian Liu

J. Chem. Phys. 131, 244113 (2009); http://dx.doi.org/10.1063/1.3283036 (12 pages) | Cited 19 times

Online Publication Date: 30 December 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
It is recognized only recently that the incorporation of the magnetic balance condition is absolutely essential for four-component relativistic theories of magnetic properties. Another important issue to be handled is the so-called gauge problem in calculations of, e.g., molecular magnetic shielding tensors with finite bases. It is shown here that the magnetic balance can be adapted to distributed gauge origins, leading to, e.g., magnetically balanced gauge-including atomic orbitals (MB-GIAOs) in which each magnetically balanced atomic orbital has its own local gauge origin placed on its center. Such a MB-GIAO scheme can be combined with any level of theory for electron correlation. The first implementation is done here at the coupled-perturbed Dirac–Kohn–Sham level. The calculated molecular magnetic shielding tensors are not only independent of the choice of gauge origin but also converge rapidly to the basis set limit. Close inspections reveal that (zeroth order) negative energy states are only important for the expansion of first order electronic core orbitals. Their contributions to the paramagnetism are therefore transferable from atoms to molecule and are essentially canceled out for chemical shifts. This allows for simplifications of the coupled-perturbed equations.
Show PACS
33.25.+k Nuclear resonance and relaxation
31.15.ve Electron correlation calculations for atoms and ions: ground state
31.15.aj Relativistic corrections, spin-orbit effects, fine structure; hyperfine structure

Competition between current-induced excitation and bath-induced decoherence in molecular junctions

Ryan Jorn and Tamar Seideman

J. Chem. Phys. 131, 244114 (2009); http://dx.doi.org/10.1063/1.3276281 (17 pages) | Cited 7 times

Online Publication Date: 30 December 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A general framework is presented to describe a resonant inelastic current inducing dynamics in the nuclear degrees of freedom of a molecule embedded between two electrodes. This approach makes use of the scattering theory of density matrices to account for the interaction between the scattering charge and the molecular modes to all orders and reduces in appropriate limits to both the standard master equation treatment for vibrational heating and the Landauer formalism for purely elastic transport. While the method presented here is equivalent to these approaches in limiting cases, it also goes well beyond their restrictions by incorporating the full quantum dynamics in the vibrational subspace in the presence of tunneling current. By application to the Au–C60–Au junction, it is shown that inclusion of vibrational coherences, which were previously neglected, is crucial to accurately predict the dynamics induced by current in molecular devices. Interaction with a bath of phonon modes is incorporated within the Bloch model and the competition between the bath-induced relaxation processes and the current-induced excitation is studied in detail over a range of temperatures.
Show PACS
63.20.dd Measurements
82.45.Fk Electrodes
61.48.-c Structure of fullerenes and related hollow and planar molecular structures

Molecular modeling of intermolecular and intramolecular excluded volume interactions for polymers at interfaces

M. Charlaganov and F. A. M. Leermakers

J. Chem. Phys. 131, 244115 (2009); http://dx.doi.org/10.1063/1.3276286 (7 pages) | Cited 3 times

Online Publication Date: 30 December 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A hybrid modeling approach is proposed for inhomogeneous polymer solutions. The method is illustrated for the depletion problem with polymer chains up to N = 103 segments in semidilute solutions and good solvent conditions. In a three-dimensional volume, a set of freely jointed chains is considered for which the translational degrees of freedom are sampled using a coarse grained Monte Carlo simulation and the conformational degrees of freedom of the chains are computed using a modified self-consistent field theory. As a result, both intramolecular and intermolecular excluded volume effects are accounted for, not only for chains near the surface, but in the bulk as well. Results are consistent with computer simulations and scaling considerations. More specifically, the depletion thickness, which is a measure for the bulk correlation length, scales as δ∝φ−0.75 and converges to the mean field result in the concentrated regime.
Show PACS
61.20.Ja Computer simulation of liquid structure
61.25.he Polymer solutions

The subtleties of explicitly correlated Z-averaged perturbation theory: Choosing an R12 method for high-spin open-shell molecules

Jeremiah J. Wilke and Henry F. Schaefer

J. Chem. Phys. 131, 244116 (2009); http://dx.doi.org/10.1063/1.3269031 (10 pages) | Cited 8 times

Online Publication Date: 30 December 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Explicitly correlated MP2-R12 and coupled cluster R12 methods have proven to be effective in achieving the basis set limit of correlated wave function methods. However, correlated methods for high-spin open-shell states are typically based on semicanonical orbitals, leading to an unrestricted formalism, which for double excitations requires three independent sets of amplitudes. In contrast, Z-averaged perturbation theory redefines the Hamiltonian with a symmetric exchange operator, thereby allowing a spin-restricted formulation with equivalent α and β subspaces. In the current work, we present a preliminary study of explicitly correlated ZAPT for second-order perturbation theory. The superior basis set convergence of R12 methods is demonstrated for a set of atomization energies, showing the R12 results to be competitive with common basis set extrapolation techniques, albeit at a fraction of the cost. Given the efficiency gains associated with the symmetric exchange operator, we suggest ZAPT as a candidate for reducing the cost of current open-shell MP2-R12 and CCSD(T)-R12 computations.
Show PACS
31.15.bw Coupled-cluster theory
33.15.Fm Bond strengths, dissociation energies

Microscopic derivation of discrete hydrodynamics

Pep Español, Jesús G. Anero, and Ignacio Zúñiga

J. Chem. Phys. 131, 244117 (2009); http://dx.doi.org/10.1063/1.3274222 (15 pages) | Cited 10 times

Online Publication Date: 31 December 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
By using the standard theory of coarse graining based on Zwanzig’s projection operator, we derive the dynamic equations for discrete hydrodynamic variables. These hydrodynamic variables are defined in terms of the Delaunay triangulation. The resulting microscopically derived equations can be understood, a posteriori, as a discretization on an arbitrary irregular grid of the Navier–Stokes equations. The microscopic derivation provides a set of discrete equations that exactly conserves mass, momentum, and energy and the dissipative part of the dynamics produces strict entropy increase. In addition, the microscopic derivation provides a practical implementation of thermal fluctuations in a way that the fluctuation-dissipation theorem is satisfied exactly. This paper points toward a close connection between coarse-graining procedures from microscopic dynamics and discretization schemes for partial differential equations.
Show PACS
47.10.ad Navier-Stokes equations
65.20.-w Thermal properties of liquids

A density-functional approximation for relativistic kinetic energy

Axel D. Becke

J. Chem. Phys. 131, 244118 (2009); http://dx.doi.org/10.1063/1.3280730 (5 pages)

Online Publication Date: 31 December 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A density-functional approximation for the relativistic kinetic energy of a many-electron system is introduced, depending on the total particle density and the (nonrelativistic) kinetic energy density. The resulting scalar variational orbital equation is similar to Schrödinger’s nonrelativistic equation, but includes relativistic mass-velocity effects to all orders in p. We test the theory by computing relativistic orbitals in the uranium atom and comparing their energies and mean radii with Dirac and zeroth-order regular approximation results.
Show PACS
31.15.es Applications of density-functional theory (e.g., to electronic structure and stability; defect formation; dielectric properties, susceptibilities; viscoelastic coefficients; Rydberg transition frequencies)

Prediction of charge-transfer excitations in coumarin-based dyes using a range-separated functional tuned from first principles

Tamar Stein, Leeor Kronik, and Roi Baer

J. Chem. Phys. 131, 244119 (2009); http://dx.doi.org/10.1063/1.3269029 (5 pages) | Cited 30 times

Online Publication Date: 31 December 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We study the description of charge-transfer excitations in a series of coumarin-based donor-bridge-acceptor dyes. We show that excellent predictive power for the excitation energies and oscillator strengths in these systems is obtained by using a range-separated hybrid functional within the generalized Kohn–Sham approach to time-dependent density functional theory. Key to this success is a step for tuning the range separation parameter from first principles. We explore different methods for this tuning step, which are variants of a recently suggested approach for charge-transfer excitations [ T. Stein et al., J. Am. Chem. Soc. 131, 2818 (2009) ]. We assess the quality of prediction by comparing to excitation energies previously published for the same systems using the approximate coupled-cluster singles and doubles (CC2) method.
Show PACS
31.15.ag Excitation energies and lifetimes; oscillator strengths
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
31.15.ee Time-dependent density functional theory
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

Partial ion yield spectroscopy around the Cl 2p and C 1s ionization thresholds in CF3Cl

D. Céolin, M. N. Piancastelli, W. C. Stolte, and D. W. Lindle

J. Chem. Phys. 131, 244301 (2009); http://dx.doi.org/10.1063/1.3274642 (7 pages) | Cited 2 times

Online Publication Date: 22 December 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We present a partial ion yield experiment on freon 13, CF3Cl, excited in the vicinity of the C 1s and Cl 2p ionization thresholds. We have collected a large amount of cationic fragments and a few anionic fragments at both edges. We have observed a strong intensity dependence of Rydberg transitions with ion fragment size for the CFnCl+ and CFn+/F+ (n = 0–3) series at both the Cl 2p and C 1s ionization edges. Selectivity in the fragmentation processes involving the C–Cl and C–F bonds are highlighted by the intensities of the C 1s to lowest unoccupied molecular orbital (LUMO) and LUMO+1 transitions measured on the CFnCl+ and CFn+ yields. Equally, by comparison with their cation counterpart, we discuss possible bond-length dependence for the anion formation at the carbon 1s edge.
Show PACS
33.80.Eh Autoionization, photoionization, and photodetachment
33.70.Fd Absolute and relative line and band intensities
33.15.Dj Interatomic distances and angles
Page 1 of 4 Pages Next Page | Jump to Page
Close

Google Calendar

ADVERTISEMENT

Go to AIP Home   © AIP Publishing LLC
close