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Molecular dynamics simulations are used to study the response of a room temperature molten salt to an external electric field when it is confined to a nanoslit. The spectrum of charge density fluctuations in the bulk is used to describe the relaxation of the polarization in the confined system.

The effects of varying the relative weights of the Lennard-Jones and Coulombic contributions to the energy of the SPC/E model on its water like structural, dynamic, and thermodynamic anomalies are investigated. The results suggest that for a liquid to show negative thermal expansion and anomalous density dependence in its transport properties, it must have a local structure that differs from and is inconsistent with simple Lennard-Jones type spherical symmetry.

Simulations of a flexible model of the tri-iodide ion have been used to study the effects of temperature and solvent on the vibrational energy relaxation rate and the pure dephasing rate of the two stretching modes. These rates were determined in ethanol and 2-methyltetrahydrofuran at 100 K, 200 K, and 300 K, covering the range between glass and mobile liquid states for both solvents. In agreement with experiment the temperature dependence is small. In ethanol the symmetry of the tri-iodide ion is broken at the three temperatures studied, while in methyltetrahydrofuran symmetry is retained except at the lowest temperature. In order to examine different contributions to the relaxation processes, perturbation theory was applied to simulations with rigid ions. Although the large amplitude of the solvent-induced geometry changes suggests that perturbation theory is at best qualitative, reasonable agreement was obtained between the results from the flexible simulation and perturbation theory in 2-methyltetrahydrofuran. Both solvent-induced curvature and solvent force terms were found to contribute to the solvent frequency shifts and the pure dephasing rates. In ethanolic solutions the time correlation functions of the forces decay rapidly, but the curvature term probes a slow dynamical process. At least in our model, the lines would not be completely motionally narrowed in solution in ethanol. Comparisons are made with experiment and previous work. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The simulations of a model system of charged spherical ions in the ionic liquids dimethylimidazolium chloride ([dmim][Cl]), dimethylimidazolium hexafluorophosphate ([dmim][P[F.sub.6]]) and the polar liquid acetonitrile (MeCN) are used for examining the applicability of Marcus theory to electrochemical half-cell redox processes in these liquids. The similarities between the different types of solvent are attributed to the essentially long-range nature of the relevant interactions and the effectiveness of the screening of the ion potential.

An alternative explanation of the size-dependent maximum in ion mobility in water in terms of the levitation effect is proposed, which accounts for the observed size-dependent maximum in the ion mobility of guest diffusion in porous media. As in the levitation effect, the friction coefficient, the potential energy fluctuations, and the activation energy are found to be minima for particles with maximum self diffusivities similar to the guest diffusion in zeolites.

Studies the displacement and distortion of the ammonium ion in rotational transition states in ammonium fluoride and ammonium chloride. Computational methods; Equilibrium structure of NH[sub 4]F; Transition states in NH[sub 4]F; Transition states in NH[sub 4]Cl.

Studies the kinetics of passage of carbon dioxide and nitrogen through the liquid-vapor interface of water. Initiation of trajectories in the gas phase; Average lifetime of molecules in the surface determined to be longer than the inverse of the energy relaxation rate; Return of molecules to the gas phase.

The microscopic structural and dynamic properties of 1,3-dimethylimidazolium chloride and 1,3-dimethylimidazolium hexafluorophospate with water are investigated. The analysis of both the local structure and the dynamics of the mixtures reveal that at low concentrations water molecules are isolated or exist in small independent clusters.

Examines immersion in hydrogen-bonding solvents leading to breakage of the centro-symmetry of the tri-iodide ion by computer simulation. Fundamental problems in the simulation of the tri-iodide ion; Calculation of the polarization energy; Stability of solvated ion; Estimation of vibrational energy and phase relaxation.

Focuses on the transfer of a carbon dioxide molecule from the gas phase through a thin liquid water film supported on ionic single crystal surfaces of sodium chloride and magnesium oxide. Free energy profile for the carbon monoxide; Use of a constrained molecular dynamics technique to evaluate the free energy profile of the dynamics of mass transport of molecules.

There has been extensive study of ion mobilities in polar solvents in the bulk phase, and it is suggested that the Stokes' law breaks down in the case of small ions in highly polar solvents. Experiments show separate curves for cation and anion mobilities and it is suggested that the asymmetric charge distribution of the solvent molecule may explain this. A computer simulation study was undertaken of contributions of the frictional force on ions in aqueous solution at 25 deg C at infinite dilution.

Molecular dynamics simulation using the simple point charge model for water at 25 degrees Centigrade was used to study the mobilities of the metal cations Li+, Na+, K+, Rb+, Cs+ and Ca2+ and the halides F-, Cl-, Br- and I- at infinite dilution. The mobilities of Li+, Na+, K+, Rb+ and F- were found to increase on discharge, while Cl, Br and I showed smaller mobilities. Results also provide information on the solvation structure and dynamics of the individual cations and anions relative to their mobilities.

The structure of the gas-liquid surface of dimethylimidazolium chloride has been studied using atomistic simulation. We find that there is a region of enhanced density immediately below the interface in which the cations are oriented with their planes perpendicular to the surface and their dipoles in the surface plane. There is negligible segregation of cations and anions. The temperature dependence of the surface tension is predicted to be anomalously low or be reversed in sign. The vapour-liquid interfaces between mixtures of water and dimethylimidazolium chloride show similar regions of enhanced density and preferential orientation of the cations. Water molecules also show preferential orientation in the interface region and are preferentially adsorbed on the vapour side of the interface. The surface tension decreases with increase in the mole fraction of water. [ABSTRACT FROM AUTHOR]

A molecular dynamics model is developed to investigate the pure vibrational dephasing of I[sub 3, sup -] in solvent at temperatures ranging from room temperature to 100 K. The triiodide ion is described by a valence bond model which responds to the field of the classical solvent molecules. We find that the pure dephasing rate does not change much with temperature. This result can then be interpreted in terms of of Kubo lineshape theory. [ABSTRACT FROM AUTHOR]

Ab initio calculations of the density of states for adsorbed monolayers of water on a MgO(1 0 0) surface are compared with metastable impact electron spectra (MIES) and ultraviolet photoelectron spectra (UPS). The calculations confirm the suggested assignments and in particular show that there is good evidence that some, but not all, molecules have dissociated to hydroxide ions. Density of state calculations are shown for configurations with no dissociated molecules, one third of the molecules dissociated and half the molecules dissociated; the agreement with experiment is best for the configuration with one third of the molecules dissociated. [Copyright &y& Elsevier]