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 Sep 2008

Volume 129, Issue 12, Articles (12xxxx)

Page 1 of 4 Pages Next Page | Jump to Page
back to top
RSS Feeds

Veering the motion of a magnetic chemical locomotive in a liquid

Krishna Kanti Dey, Deepika Sharma, Saurabh Basu, and Arun Chattopadhyay

J. Chem. Phys. 129, 121101 (2008); http://dx.doi.org/10.1063/1.2985610 (4 pages) | Cited 1 time

Online Publication Date: 24 September 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The motion of micron-sized catalytic polymer beads coated with thin film or nanoparticle form of Ni in aqueous H2O2 is reported herein. In the absence of any magnetic field, the beads moved vertically upward in the medium, owing to sufficient bubbles deposited on them following catalytic decomposition of H2O2 by Ni. However, in the presence of an external magnetic field (perpendicular to the direction of motion), angular deviation in the motion is observed, with the deviations increasing with the strength of the field. The results are explained based on a model involving interaction of the beads with the external magnetic field.
Show PACS
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
75.50.Tt Fine-particle systems; nanocrystalline materials

Pinned emission from ultrasmall cadmium selenide nanocrystals

Albert D. Dukes, III, Michael A. Schreuder, Jessica A. Sammons, James R. McBride, Nathanael J. Smith, and Sandra J. Rosenthal

J. Chem. Phys. 129, 121102 (2008); http://dx.doi.org/10.1063/1.2983632 (4 pages) | Cited 5 times

Online Publication Date: 24 September 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We report pinning of the emission spectrum in ultrasmall CdSe nanocrystals with a diameter of 1.7 nm and smaller. It was observed that the first emission feature ceased to blueshift once the band edge absorption reached 420 nm, though the band edge absorption continued to blueshift with decreasing nanocrystal diameter.
Show PACS
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Et II-VI semiconductors
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.20.At Surface states, band structure, electron density of states

One-dimensional tunneling calculations in the imaginary-frequency, rectilinear saddle-point normal mode

Yimin Wang and Joel M. Bowman

J. Chem. Phys. 129, 121103 (2008); http://dx.doi.org/10.1063/1.2978230 (5 pages) | Cited 8 times

Online Publication Date: 25 September 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We present tunneling calculations using the reaction path Hamiltonian in the zero-curvature approximation and a one-dimensional Hamiltonian in the imaginary-frequency, rectilinear normal mode of a saddle point, neglecting the vibrational angular momentum terms. This latter Hamiltonian was recently introduced and applied to the tunneling splitting in full-dimensional malonaldeyde [ Y. Wang et al., J. Chem. Phys. 128, 224314 (2008) ]. The results using the latter method are shown to be much more accurate than those using the former one for the ground-state tunneling splittings for H and D-transfer in malonaldehyde and for the D+H2 reaction in three dimensions for zero total angular momentum.
Show PACS
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
82.20.Kh Potential energy surfaces for chemical reactions
71.15.-m Methods of electronic structure calculations

Fractional spins and static correlation error in density functional theory

Aron J. Cohen, Paula Mori-Sánchez, and Weitao Yang

J. Chem. Phys. 129, 121104 (2008); http://dx.doi.org/10.1063/1.2987202 (4 pages) | Cited 27 times

Online Publication Date: 26 September 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Electronic states with fractional spins arise in systems with large static correlation (strongly correlated systems). Such fractional-spin states are shown to be ensembles of degenerate ground states with normal spins. It is proven here that the energy of the exact functional for fractional-spin states is a constant, equal to the energy of the comprising degenerate pure-spin states. Dramatic deviations from this exact constancy condition exist with all approximate functionals, leading to large static correlation errors for strongly correlated systems, such as chemical bond dissociation and band structure of Mott insulators. This is demonstrated with numerical calculations for several molecular systems. Approximating the constancy behavior for fractional spins should be a major aim in functional constructions and should open the frontier for density functional theory to describe strongly correlated systems. The key results are also shown to apply in reduced density-matrix functional theory.
Show PACS
31.15.aq Strongly correlated electron systems: generalized tight-binding method
33.15.Bh General molecular conformation and symmetry; stereochemistry
31.15.E- Density-functional theory

Nonlinear Poisson–Boltzmann model of charged lipid membranes: Accounting for the presence of zwitterionic lipids

Demmelash H. Mengistu and Sylvio May

J. Chem. Phys. 129, 121105 (2008); http://dx.doi.org/10.1063/1.2990746 (3 pages) | Cited 4 times

Online Publication Date: 29 September 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The nonlinear Poisson–Boltzmann model is used to derive analytical expressions for the free energies of both mixed anionic-zwitterionic and mixed cationic-zwitterionic lipid membranes as function of the mole fraction of charged lipids. Accounting explicitly for the electrostatic properties of the zwitterionic lipid species affects the free energy of anionic and cationic membranes in a qualitatively different way: That of an anionic membrane changes monotonously as a function of the mole fraction of charged lipids, whereas it passes through a pronounced minimum for a cationic membrane.
Show PACS
87.14.Cc Lipids
87.16.D- Membranes, bilayers, and vesicles
87.15.kt Protein-membrane interactions
82.39.Jn Charge (electron, proton) transfer in biological systems

Diffusive motions in liquid medium-chain n-alkanes as seen by quasielastic time-of-flight neutron spectroscopy

Tobias Unruh, Christoph Smuda, Sebastian Busch, Jürgen Neuhaus, and Winfried Petry

J. Chem. Phys. 129, 121106 (2008); http://dx.doi.org/10.1063/1.2990026 (4 pages) | Cited 1 time

Online Publication Date: 30 September 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Different diffusive motions in liquid C32H66 on a picosecond time scale could be disentangled by resolution resolved quasielastic time-of-flight neutron spectroscopy (QENS). It is demonstrated that at all observation times, the dominating motion causes a Q2 proportionality of the QENS signal, which indicates a Fickian diffusion mechanism. The observed motions can be characterized by an observation time dependent apparent diffusion coefficient Da(to), which is up to one order of magnitude larger than the molecular self-diffusion coefficient Ds. By comparison with molecular dynamics simulations, the identified motions are attributed to displacements of hydrogen atoms reflecting not only global but also local molecular trajectories. Despite the rodlike shape of the molecules, the center of mass diffusion was found to be essentially isotropic. A coherent picture of the diffusional processes ranging from the fast tumbling of CH2 groups to the slow long range molecular diffusion is presented.
Show PACS
66.10.cg Mass diffusion, including self-diffusion, mutual diffusion, tracer diffusion, etc.
61.20.Ja Computer simulation of liquid structure
61.25.-f Studies of specific liquid structures

Translocation of a knotted polypeptide through a pore

Lei Huang and Dmitrii E. Makarov

J. Chem. Phys. 129, 121107 (2008); http://dx.doi.org/10.1063/1.2968554 (4 pages) | Cited 10 times

Online Publication Date: 30 September 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We use Langevin dynamics simulations to study how the presence of a deep knot affects the time it takes to thread a polypeptide chain through a narrow pore by pulling mechanically at its end. The polypeptide was designed to contain a knotted unstructured segment inserted between two β-hairpins, which prevented the knot from slipping off the chain ends. In the range of forces studied (40–200 pN), the mean translocation time increased with the knot complexity. The type 52 knot, which was recently discovered in the structure of human ubiquitin hydrolase and is the most complex knot found in the protein databank, slows down translocation by about two orders of magnitude, as compared to the unknotted chain. In contrast to the unknotted chain case, the translocation mechanism of knotted chains involves multiple slippage events suggesting that the corresponding free energy landscape is rugged and involves multiple metastable minima.
Show PACS
87.15.B- Structure of biomolecules
87.15.H- Dynamics of biomolecules
87.15.A- Theory, modeling, and computer simulation
36.20.Ey Conformation (statistics and dynamics)
back to top
RSS Feeds
back to top Theoretical Methods and Algorithms

Efficient and robust quantum Monte Carlo estimate of the total and spin electron densities at nuclei

P. Håkansson and Massimo Mella

J. Chem. Phys. 129, 124101 (2008); http://dx.doi.org/10.1063/1.2982930 (11 pages) | Cited 1 time

Online Publication Date: 22 September 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The computational performance of two different variational quantum Monte Carlo estimators for both the electron and spin densities on top of nuclei are tested on a set of atomic systems containing also third-row species. Complications due to an unbounded variance present for both estimators are circumvented using appropriate sampling strategies. Our extension of a recently proposed estimator [ Phys. Rev. A 69, 022701 (2004) ] to deal with heavy fermionic systems appears to provide improved computational efficiency, at least an order of magnitude, with respect to alternative literature approaches for our test set. Given the importance of an adequate sampling of the core region in computing the electron density at a nucleus, a further reduction in the overall simulation cost is obtained by employing accelerated sampling algorithms.
Show PACS
31.15.bt Statistical model calculations (including Thomas-Fermi and Thomas-Fermi-Dirac models)
31.10.+z Theory of electronic structure, electronic transitions, and chemical binding
05.30.Fk Fermion systems and electron gas
31.15.xt Variational techniques

Laser-induced nuclear magnetic resonance splitting in hydrocarbons

Suvi Ikäläinen, Perttu Lantto, Pekka Manninen, and Juha Vaara

J. Chem. Phys. 129, 124102 (2008); http://dx.doi.org/10.1063/1.2977741 (8 pages) | Cited 6 times

Online Publication Date: 22 September 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Irradiation of matter with circularly polarized light (CPL) shifts all nuclear magnetic resonance (NMR) lines. The phenomenon arises from the second-order interaction of the electron cloud with the optical field, combined with the orbital hyperfine interaction. The shift occurs in opposite directions for right and left CPL, and rapid switching between them will split the resonance lines into two. We present ab initio and density functional theory predictions of laser-induced NMR splittings for hydrocarbon systems with different sizes: ethene, benzene, coronene, fullerene, and circumcoronene. Due to the computationally challenging nature of the effect, traditional basis sets could not be used for the larger systems. A novel method for generating basis sets, mathematical completeness optimization, was employed. As expected, the magnitude of the spectral splitting increases with the laser beam frequency and polarizability of the system. Massive amplification of the effect is also observed close to the optical excitation energies. A much larger laser-induced splitting is found for the largest of the present molecules than for the previously investigated noble gas atoms or small molecules. The laser intensity required for experimental detection of the effect is discussed.
Show PACS
33.25.+k Nuclear resonance and relaxation
33.70.Jg Line and band widths, shapes, and shifts
33.15.Pw Fine and hyperfine structure
31.15.aj Relativistic corrections, spin-orbit effects, fine structure; hyperfine structure
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)

Hybrid functionals with local range separation

Aliaksandr V. Krukau, Gustavo E. Scuseria, John P. Perdew, and Andreas Savin

J. Chem. Phys. 129, 124103 (2008); http://dx.doi.org/10.1063/1.2978377 (7 pages) | Cited 29 times

Online Publication Date: 23 September 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Range-separated (screened) hybrid functionals provide a powerful strategy for incorporating nonlocal exact (Hartree–Fock-type) exchange into density functional theory. Existing implementations of range separation use a fixed system-independent screening parameter. Here, we propose a novel method that uses a position-dependent screening function. These locally range-separated hybrids add substantial flexibility for describing diverse electronic structures and satisfy a high-density scaling constraint better than the fixed screening approximation does.
Show PACS
31.15.eg Exchange-correlation functionals (in current density functional theory)
31.15.xr Self-consistent-field methods

Determining quasidiabatic coupled electronic state Hamiltonians using derivative couplings: A normal equations based method

Brian N. Papas, Michael S. Schuurman, and David R. Yarkony

J. Chem. Phys. 129, 124104 (2008); http://dx.doi.org/10.1063/1.2978389 (10 pages) | Cited 18 times

Online Publication Date: 23 September 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A self-consistent procedure for constructing a quasidiabatic Hamiltonian representing Nstate coupled electronic states in the vicinity of an arbitrary point in nuclear coordinate space is described. The matrix elements of the Hamiltonian are polynomials of arbitrary order. Employing a crude adiabatic basis, the coefficients of the linear terms are determined exactly using analytic gradient techniques. The remaining polynomial coefficients are determined from the normal form of a system of pseudolinear equations, which uses energy gradient and derivative coupling information obtained from reliable multireference configuration interaction wave functions. In a previous implementation energy gradient and derivative coupling information were employed to limit the number of nuclear configurations at which ab initio data were required to determine the unknown coefficients. Conversely, the key aspect of the current approach is the use of ab initio data over an extended range of nuclear configurations. The normal form of the system of pseudolinear equations is introduced here to obtain a least-squares fit to what would have been an (intractable) overcomplete set of data in the previous approach. This method provides a quasidiabatic representation that minimizes the residual derivative coupling in a least-squares sense, a means to extend the domain of accuracy of the diabatic Hamiltonian or refine its accuracy within a given domain, and a way to impose point group symmetry and hermiticity. These attributes are illustrated using the 1 2A1 and 1 2E states of the 1-propynyl radical, CH3CC.
Show PACS
31.15.xr Self-consistent-field methods
31.15.am Relativistic configuration interaction (CI) and many-body perturbation calculations

Statistically optimal analysis of samples from multiple equilibrium states

Michael R. Shirts and John D. Chodera

J. Chem. Phys. 129, 124105 (2008); http://dx.doi.org/10.1063/1.2978177 (10 pages) | Cited 66 times

Online Publication Date: 23 September 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We present a new estimator for computing free energy differences and thermodynamic expectations as well as their uncertainties from samples obtained from multiple equilibrium states via either simulation or experiment. The estimator, which we call the multistate Bennett acceptance ratio estimator (MBAR) because it reduces to the Bennett acceptance ratio estimator (BAR) when only two states are considered, has significant advantages over multiple histogram reweighting methods for combining data from multiple states. It does not require the sampled energy range to be discretized to produce histograms, eliminating bias due to energy binning and significantly reducing the time complexity of computing a solution to the estimating equations in many cases. Additionally, an estimate of the statistical uncertainty is provided for all estimated quantities. In the large sample limit, MBAR is unbiased and has the lowest variance of any known estimator for making use of equilibrium data collected from multiple states. We illustrate this method by producing a highly precise estimate of the potential of mean force for a DNA hairpin system, combining data from multiple optical tweezer measurements under constant force bias.
Show PACS
31.15.bt Statistical model calculations (including Thomas-Fermi and Thomas-Fermi-Dirac models)
05.70.Ce Thermodynamic functions and equations of state
02.50.-r Probability theory, stochastic processes, and statistics

The augmented Roothaan–Hall method for optimizing Hartree–Fock and Kohn–Sham density matrices

Stinne Høst, Jeppe Olsen, Branislav Jansík, Lea Thøgersen, Poul Jørgensen, and Trygve Helgaker

J. Chem. Phys. 129, 124106 (2008); http://dx.doi.org/10.1063/1.2974099 (12 pages) | Cited 5 times

Online Publication Date: 24 September 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We present a novel method for the optimization of Hartree–Fock and Kohn–Sham energies that does not suffer from the flaws of the conventionally used two-step Roothaan–Hall (RH) with direct inversion in iterative subspace (DIIS) acceleration scheme, improving the reliability of the optimization while reducing its cost. The key to its success is the replacement of the two separate steps of each RH/DIIS iteration by a single concerted step that fully exploits the Hessian information available from the previous iterations. It is a trust-region based method and therefore by design converges to an energy minimum. Numerical examples are given to illustrate that the algorithm is robust and cost efficient, converging smoothly to a minimum also in cases when the RH/DIIS algorithm fails to converge or when it converges to a saddle point rather than to a minimum. The algorithm is based on matrix multiplications and becomes linearly scaling for sufficiently large systems.
Show PACS
31.15.xr Self-consistent-field methods

On the simulated scaling based free energy simulations: Adaptive optimization of the scaling parameter intervals

Lianqing Zheng and Wei Yang

J. Chem. Phys. 129, 124107 (2008); http://dx.doi.org/10.1063/1.2982161 (5 pages) | Cited 5 times

Online Publication Date: 25 September 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Recently, we developed a generalized ensemble based free energy simulation technique, the simulated scaling (SS) method [ Li et al., J. Chem. Phys. 126, 024106 (2007) ]. In the SS simulations, random walks in the scaling parameter space are realized and free energy values can be conveniently estimated based on trial biasing weights. To improve free energy convergence in the SS simulations, we adopt a recent adaptive algorithm to systematically optimize the scaling parameter intervals; here, the optimization target is the round-trip rate between two end chemical states. As demonstrated in our model studies on the solvation of chloride ion and methane, free energy convergence can be greatly improved when the round-trip rates are accelerated.
Show PACS
05.70.Ce Thermodynamic functions and equations of state
02.60.Pn Numerical optimization

Mixed time-dependent density-functional theory/classical trajectory surface hopping study of oxirane photochemistry

Enrico Tapavicza, Ivano Tavernelli, Ursula Rothlisberger, Claudia Filippi, and Mark E. Casida

J. Chem. Phys. 129, 124108 (2008); http://dx.doi.org/10.1063/1.2978380 (19 pages) | Cited 26 times

Online Publication Date: 25 September 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We present a mixed time-dependent density-functional theory (TDDFT)/classical trajectory surface hopping (SH) study of the photochemical ring opening in oxirane. Previous preparatory work limited to the symmetric CC ring-opening pathways of oxirane concluded that the Tamm-Dancoff approximation (TDA) is important for improving the performance of TDDFT away from the equilibrium geometry. This observation is supported by the present TDDFT TDA/SH calculations which successfully confirm the main experimentally derived Gomer-Noyes mechanism for the photochemical CO ring opening of oxirane and, in addition, provide important state-specific information not easily accessible from experiments. In particular, we find that, while one of the lowest two excited states is photochemically relatively inert, excitation into the other excited state leads predominantly to rapid ring opening, cyclic-C2H4O→•CH2CH2O•. This is followed by hopping to the electronic ground state where hot (4000 K) dynamics leads to further reactions, namely, •CH2CH2O•→CH3CHO→•CH3+•CHO and CH4+CO. We note that, in the dynamics, we are not limited to following minimum energy pathways and several surface hops may actually be needed before products are finally reached. The performance of different functionals is then assessed by comparison of TDDFT and diffusion Monte Carlo potential energy curves along a typical TDDFT TDA/SH reaction path. Finally, although true (S0,S1) conical intersections are expected to be absent in adiabatic TDDFT, we show that the TDDFT TDA is able to approximate a conical intersection in this system.
Show PACS
82.50.-m Photochemistry
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.20.Kh Potential energy surfaces for chemical reactions
31.50.Df Potential energy surfaces for excited electronic states
31.50.Bc Potential energy surfaces for ground electronic states

Effect of the nonlocal exchange on the performance of the orbital-dependent correlation functionals from second-order perturbation theory

Igor V. Schweigert and Rodney J. Bartlett

J. Chem. Phys. 129, 124109 (2008); http://dx.doi.org/10.1063/1.2978171 (8 pages) | Cited 1 time

Online Publication Date: 25 September 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Adding a fraction of the nonlocal exchange operator to the local orbital-dependent exchange potential improves the many-body perturbation expansion based on the Kohn–Sham determinant. The effect of such a hybrid scheme on the performance of the orbital-dependent correlation functional from the second-order perturbation theory (PT2H) is investigated numerically. A small fraction of the nonlocal exchange is often sufficient to ensure the existence of the self-consistent solution for the PT2H potential. In the He and Be atoms, including 37% of the nonlocal exchange leads to the correlation energies and electronic densities that are very close to the exact ones. In molecules, varying the fraction of the nonlocal exchange may result in the PT2H energy closely reproducing the CCSD(T) value; however such a fraction depends on the system and does not always result in an accurate electronic density. We also numerically verify that the “semicanonical” perturbation series includes most of the beneficial effects of the nonlocal exchange without sacrificing the locality of the exchange potential.
Show PACS
31.15.xp Perturbation theory
31.15.eg Exchange-correlation functionals (in current density functional theory)
31.15.bw Coupled-cluster theory

Self-consistent generalized Kohn-Sham local hybrid functionals of screened exchange: Combining local and range-separated hybridization

Benjamin G. Janesko, Aliaksandr V. Krukau, and Gustavo E. Scuseria

J. Chem. Phys. 129, 124110 (2008); http://dx.doi.org/10.1063/1.2980056 (9 pages) | Cited 20 times

Online Publication Date: 29 September 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We present local hybrid functionals that incorporate a position-dependent admixture of short-range (screened) nonlocal exact [Hartree-Fock-type (HF)] exchange. We test two limiting cases: screened local hybrids with no long-range HF exchange and long-range-corrected local hybrids with 100% long-range HF exchange. Long-range-corrected local hybrids provide the exact asymptotic exchange-correlation potential in finite systems, while screened local hybrids avoid the problems inherent to long-range HF exchange in metals and small-bandgap systems. We treat these functionals self-consistently using the nonlocal exchange potential constructed from Kohn-Sham orbital derivatives. Generalized Kohn-Sham calculations with screened and long-range-corrected local hybrids can provide accurate molecular thermochemistry and kinetics, comparable to existing local hybrids of full-range exchange. Generalized Kohn-Sham calculations with existing full-range local hybrids provide results consistent with previous non-self-consistent and “localized local hybrid” calculations. These new functionals appear to provide a promising extension of existing local and range-separated hybrids.
Show PACS
31.15.E- Density-functional theory
31.15.xr Self-consistent-field methods

Linearized semiclassical initial value time correlation functions with maximum entropy analytic continuation

Jian Liu and William H. Miller

J. Chem. Phys. 129, 124111 (2008); http://dx.doi.org/10.1063/1.2981065 (17 pages) | Cited 15 times

Online Publication Date: 29 September 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The maximum entropy analytic continuation (MEAC) method is used to extend the range of accuracy of the linearized semiclassical initial value representation (LSC-IVR)/classical Wigner approximation for real time correlation functions. LSC-IVR provides a very effective “prior” for the MEAC procedure since it is very good for short times, exact for all time and temperature for harmonic potentials (even for correlation functions of nonlinear operators), and becomes exact in the classical high temperature limit. This combined MEAC+LSC/IVR approach is applied here to two highly nonlinear dynamical systems, a pure quartic potential in one dimensional and liquid para-hydrogen at two thermal state points (25 and 14 K under nearly zero external pressure). The former example shows the MEAC procedure to be a very significant enhancement of the LSC-IVR for correlation functions of both linear and nonlinear operators, and especially at low temperature where semiclassical approximations are least accurate. For liquid para-hydrogen, the LSC-IVR is seen already to be excellent at T = 25 K, but the MEAC procedure produces a significant correction at the lower temperature (T = 14 K). Comparisons are also made as to how the MEAC procedure is able to provide corrections for other trajectory-based dynamical approximations when used as priors.
Show PACS
82.20.Wt Computational modeling; simulation
82.20.Sb Correlation function theory of rate constants and its applications
82.20.Xr Quantum effects in rate constants (tunneling, resonances, etc.)
82.20.Ln Semiclassical theory of reactions and/or energy transfer
05.70.Ce Thermodynamic functions and equations of state
05.45.-a Nonlinear dynamics and chaos

Rydberg energies using excited state density functional theory

Chiao-Lun Cheng, Qin Wu, and Troy Van Voorhis

J. Chem. Phys. 129, 124112 (2008); http://dx.doi.org/10.1063/1.2977989 (9 pages) | Cited 7 times

Online Publication Date: 29 September 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We utilize excited state density functional theory (eDFT) to study Rydberg states in atoms. We show both analytically and numerically that semilocal functionals can give quite reasonable Rydberg energies from eDFT, even in cases where time dependent density functional theory (TDDFT) fails catastrophically. We trace these findings to the fact that in eDFT the Kohn–Sham potential for each state is computed using the appropriate excited state density. Unlike the ground state potential, which typically falls off exponentially, the sequence of excited state potentials has a component that falls off polynomially with distance, leading to a Rydberg-type series. We also address the rigorous basis of eDFT for these systems. Perdew and Levy have shown using the constrained search formalism that every stationary density corresponds, in principle, to an exact stationary state of the full many-body Hamiltonian. In the present context, this means that the excited state DFT solutions are rigorous as long as they deliver the minimum noninteracting kinetic energy for the given density. We use optimized effective potential techniques to show that, in some cases, the eDFT Rydberg solutions appear to deliver the minimum kinetic energy because the associated density is not pure state v-representable. We thus find that eDFT plays a complementary role to constrained DFT: The former works only if the excited state density is not the ground state of some potential while the latter applies only when the density is a ground state density.
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)
32.80.Ee Rydberg states
31.50.Df Potential energy surfaces for excited electronic states

Quantum streamlines within the complex quantum Hamilton–Jacobi formalism

Chia-Chun Chou and Robert E. Wyatt

J. Chem. Phys. 129, 124113 (2008); http://dx.doi.org/10.1063/1.2977747 (12 pages) | Cited 4 times

Online Publication Date: 30 September 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Quantum streamlines are investigated in the framework of the quantum Hamilton–Jacobi formalism. The local structures of the quantum momentum function (QMF) and the Pólya vector field near a stagnation point or a pole are analyzed. Streamlines near a stagnation point of the QMF may spiral into or away from it, or they may become circles centered on this point or straight lines. Additionally, streamlines near a pole display east-west and north-south opening hyperbolic structure. On the other hand, streamlines near a stagnation point of the Pólya vector field for the QMF display general hyperbolic structure, and streamlines near a pole become circles enclosing the pole. Furthermore, the local structures of the QMF and the Pólya vector field around a stagnation point are related to the first derivative of the QMF; however, the magnitude of the asymptotic structures for these two fields near a pole depends only on the order of the node in the wave function. Two nonstationary states constructed from the eigenstates of the harmonic oscillator are used to illustrate the local structures of these two fields and the dynamics of the streamlines near a stagnation point or a pole. This study presents the abundant dynamics of the streamlines in the complex space for one-dimensional time-dependent problems.
Show PACS
31.15.X- Alternative approaches
03.65.Ta Foundations of quantum mechanics; measurement theory
03.65.Ge Solutions of wave equations: bound states

An improved variational approach to off-diagonal exciton-phonon coupling

Yang Zhao, Guangqi Li, Jin Sun, and Weihua Wang

J. Chem. Phys. 129, 124114 (2008); http://dx.doi.org/10.1063/1.2987364 (10 pages) | Cited 7 times

Online Publication Date: 30 September 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A state-of-the-art variational wave function incorporating Jastrow-type exciton-phonon correlations, the global-local Ansatz, is utilized to elucidate exciton-phonon correlations in a generalized form of the Holstein Hamiltonian with the simultaneous presence of diagonal and off-diagonal exciton-phonon coupling. Much lowered ground-state energies are found for the global-local Ansatz when compared with the previously studied Toyozawa Ansatz. A three-dimensional phase diagram spanned by the transfer integral and two forms of exciton-phonon coupling is given to illustrate polaronic self-trapping near the zone center.
Show PACS
63.20.kd Phonon-electron interactions
71.38.Ht Self-trapped or small polarons

The Prigogine–Defay ratio and the microscopic theory of supercooled liquids

R. M. Pick

J. Chem. Phys. 129, 124115 (2008); http://dx.doi.org/10.1063/1.2969899 (7 pages) | Cited 2 times

Online Publication Date: 30 September 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Prigogine–Defay ratios and, more recently, their frequency extension have been proposed to be a measure of the number of nonmacroscopic processes involved in the relaxation dynamics of supercooled liquids. We show that the microscopic theory of the Navier–Stokes equations of those liquids provides a consistent thermodynamic framework in which all possible dynamical Prigogine–Defay ratios can be expressed in terms of the same relaxation functions and that these ratios provide less information than the microscopic theory itself. The latter shows that more than one relaxation process is certainly always involved in this relaxation dynamics, whatever is the molecular dynamics, or experimental, technique used to determine the latter.
Show PACS
61.20.Ja Computer simulation of liquid structure
61.20.Gy Theory and models of liquid structure
65.20.De General theory of thermodynamic properties of liquids, including computer simulation
66.20.-d Viscosity of liquids; diffusive momentum transport

Partial multicanonical algorithm for molecular dynamics and Monte Carlo simulations

Hisashi Okumura

J. Chem. Phys. 129, 124116 (2008); http://dx.doi.org/10.1063/1.2970883 (9 pages) | Cited 1 time

Online Publication Date: 30 September 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Partial multicanonical algorithm is proposed for molecular dynamics and Monte Carlo simulations. The partial multicanonical simulation samples a wide range of a part of the potential-energy terms, which is necessary to sample the conformational space widely, whereas a wide range of total potential energy is sampled in the multicanonical algorithm. Thus, one can concentrate the effort to determine the weight factor only on the important energy terms in the partial multicanonical simulation. The partial multicanonical, multicanonical, and canonical molecular dynamics algorithms were applied to an alanine dipeptide in explicit water solvent. The canonical simulation sampled the states of PII, C5, αR, and αP. The multicanonical simulation covered the αL state as well as these states. The partial multicanonical simulation also sampled the C7ax state in addition to the states that were sampled by the multicanonical simulation. In the partial multicanonical simulation, furthermore, backbone dihedral angles ϕ and ψ rotated more frequently than those in the multicanonical and canonical simulations. These results mean that the partial multicanonical algorithm has a higher sampling efficiency than the multicanonical and canonical algorithms.
Show PACS
87.15.ak Monte Carlo simulations
87.15.ap Molecular dynamics simulation
82.37.-j Single molecule kinetics

Fourier–Legendre expansion of the one-electron density matrix of ground-state two-electron atoms

Sébastien Ragot and María Belén Ruiz

J. Chem. Phys. 129, 124117 (2008); http://dx.doi.org/10.1063/1.2981526 (10 pages) | Cited 2 times

Online Publication Date: 30 September 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The density matrix ρ(r,r′) of a spherically symmetric system can be expanded as a Fourier–Legendre series of Legendre polynomials Pl(cos θ = r⋅r′/rr′). Application is here made to harmonically trapped electron pairs (i.e., Moshinsky’s and Hooke’s atoms), for which exact wavefunctions are known, and to the helium atom, using a near-exact wavefunction. In the present approach, generic closed form expressions are derived for the series coefficients of ρ(r,r′). The series expansions are shown to converge rapidly in each case, with respect to both the electron number and the kinetic energy. In practice, a two-term expansion accounts for most of the correlation effects, so that the correlated density matrices of the atoms at issue are essentially a linear functions of Pl(cos θ) = cos θ. For example, in the case of Hooke’s atom, a two-term expansion takes in 99.9% of the electrons and 99.6% of the kinetic energy. The correlated density matrices obtained are finally compared to their determinantal counterparts, using a simplified representation of the density matrix ρ(r,r′), suggested by the Legendre expansion. Interestingly, two-particle correlation is shown to impact the angular delocalization of each electron, in the one-particle space spanned by the r and r′ variables.
Show PACS
31.15.ve Electron correlation calculations for atoms and ions: ground state
02.10.De Algebraic structures and number theory
02.30.Lt Sequences, series, and summability
02.30.Mv Approximations and expansions
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

Microwave spectroscopy of the PBr radical in the X 3Σ− state

Toshiaki Okabayashi, Hideaki Kawajiri, Michiaki Umeyama, Chihiro Ide, Sumio Oe, and Mitsutoshi Tanimoto

J. Chem. Phys. 129, 124301 (2008); http://dx.doi.org/10.1063/1.2977732 (8 pages)

Online Publication Date: 22 September 2008

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The microwave spectrum of the PBr radical in the X 3Σ− ground electronic state has been observed by a source modulated spectrometer. The PBr radical was generated in a free space cell by an ac∕dc glow discharge in a mixture of PBr3 with He and∕or H2. A spectrum with three spin components for each of the two isotopomers, P79Br and P81Br, was observed. The spectrum showed hyperfine splitting caused by interactions due to both bromine and phosphorus nuclei. The molecular constants including the magnetic hyperfine and nuclear quadrupole hyperfine interaction constants were determined by analyzing the observed spectrum. The spin density of the unpaired electrons was estimated from the observed hyperfine coupling constants to be 85.4% and 16.3% on the phosphorus and bromine atoms, respectively.
Show PACS
33.20.Bx Radio-frequency and microwave spectra
33.15.Pw Fine and hyperfine structure
33.25.+k Nuclear resonance and relaxation
Page 1 of 4 Pages Next Page | Jump to Page
Close

Google Calendar

ADVERTISEMENT

Your Recent History Recent History Help

Recently Viewed

  1. Benchmarks for electronically excited states: Time-dependent density functional theory and density functional theory based multireference configuration interaction
  2. Do ionic and hydrophobic probes sense similar microenvironment in Triton X-100 nonionic reverse micelles?
  3. Energy-dependent dynamics of large-ΔE collisions: Highly vibrationally excited azulene (E = 20 390 and 38 580 cm−1) with CO2
  4. On the pressure-induced loss of crystallinity in orthophosphates of zinc and calcium
  5. Theoretical consideration of bulk free-radical copolymerization with allowance for the preferential sorption of monomers into globular nanoreactors
Go to AIP Home
Copyright © American Institute of Physics
close