Molecular dynamics simulations of Li+BF4 - in liquid ethylene carbonate, propylene carbonate, and dimethyl carbonate at low concentration are reported. Structural, thermodynamical, and dynamical properties have been obtained at 323 and 348 K in ethylene carbonate, 298 and 323 K in propylene carbonate, and 298 K in dimethyl carbonate. The diffusion coefficient of the lithium cation is found to be very similar in the three solvents ((0.3−0.6) × 10-9 m2 s-1 in this temperature range). This behavior is linked to the structure of the first solvation shell, which contains four strongly bound solvent molecules in a tetrahedral arrangement in all three cases. No exchange of solvent molecules between the first and the second solvation shells of the lithium ion have been observed during the 100-ps simulations. In the three carbonates, the fluoroborate ion is bound to 19 or 20 solvent molecules in the first solvation shell, the coordination shell being much less structured than in the case of the lithium ion, and the diffusion coefficient exhibits a more significant solvent and temperature dependence.

Two new parametrizations of a recent ab initio polarizable anisotropic site potential for water are presented. The new versions improve the description of the electrostatic interactions, add an explicit charge-transfer term, and use more accurate dispersion coefficients from the recent literature. To assess the merits of the new models, the potential energy surface of the dimer is analyzed and a comparison is made with 12 other polarizable potentials for water in the literature, most of them being currently used in computer simulation. The structure, energy, and harmonic intermolecular frequencies of the stationary points have been determined and compared with the best available ab initio calculations. The energy barriers and pathways for hydrogen atom interchange within the dimer are discussed. The second virial coefficient B(T) of steam between 373 and 973 K, including first-order quantum corrections, is reported. For all the models, the quantum corrections are found to be significant at the lowest temperatures, amounting to 10−15% at 373 K. Roughly 90% of the quantum corrections arise from the rotational degrees of freedom. Among the potentials considered, only those presented in the present work and a few others are really successful in reproducing the experimental results for B(T) in that temperature range.

The potential of mean force of two rigid guanidinium ions constrained to remain parallel is investigated in liquid water by means of free energy perturbation (FEP) molecular dynamics simulations, using various intermolecular potentials. The first simulation is carried out employing the Amber force field and the transferable intermolecular potential TIP3P water model. The second simulation is performed with the extended simple point charge SPC/E water model. In a third simulation, the polarizability of the water molecule is introduced via the use of the polarizable simple point charge model PSPC, whereas for the ions, distributed polarizabilities derived from the topological partitioning of electrostatic properties (TPEP) are incorporated on heavy atoms. For the last two simulations, atom−atom Lennard-Jones parameters and charges are derived from ab initio calculations on monomers and guanidinium−water pairs. The comparison with a previous simulation using the transferable intermolecular potential TIP4P, by Boudon et al. (J. Phys. Chem. 1990, 94, 6056−61), reveals that (i) all the models predict a stable contact ion pair (CIP) at a distance of 3.0−3.4 Å, and a solvent-separated ion pair (SSIP) at about 6.5 Å, (ii) the stabilization energy of the CIP is strongly model-dependent, varying from 10.0 kcal·mol-1, for the TIP4P model to 4.7 and 2.7 kcal·mol-1 for the SPC/E and PSPC models respectively, and (iii) in all cases, the SSIP free energy minimum is very shallow and nearly disappears for the simulation using a polarizable model. Consideration of the distribution and the orientation of the solvent molecules around the ions for the non-polarizable (SPC/E) and the polarizable (PSPC) cases does not reveal any significant difference between the two models.

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This present paper is aimed at discussing the state of aggregation in supercritical ethanol using infrared and Raman spectroscopies. A quantitative band shape analysis of the spectra associated with the OH stretching mode of ethanol has been done using IR and Raman activities determined by ab initio calculations on small oligomers. Such a methodology allows the quantification of the degree of hydrogen bonding (η), and both IR and Raman techniques lead to comparable results. This study shows that hydrogen bonds still exist in supercritical ethanol. The degree of hydrogen bonding (η) is found to be relatively constant above the critical density and strongly diminishes below it. The determined values of η are consistent with literature measurements reported using IR spectroscopy. The disagreement observed with NMR experiments has been critically discussed.

Clathrates hydrates are nanoporous crystalline materials made of water cages encapsulating guest molecules. By inserting H2 molecules with the help of a promoter (tetrahydrofuran, noted THF), systems relevant for hydrogen storage application are formed by using relatively soft pressure (of the order of 100 bar) near room temperature. Dynamic properties of hydrogen molecules confined in the small cages of the deuterated THF clathrate hydrate have been investigated at equilibrium by means of incoherent quasi-elastic neutron scattering (QENS). These QENS investigations provide direct experimental evidence about the fundamental aspect of translational diffusive motions of the hydrogen molecules. A comprehensive study of the hydrogen molecules dynamics above 100 K has been achieved through a quantitative analysis of the structure factors (i.e., the spatial extend of the H2 diffusive motion) as well as of the QENS broadening (i.e., the characteristic time of the diffusive motion). On the probed time scale, the H2 molecular translations occur within localized spherical area in the cage with low activation energy of 1.59 ± 0.06 kJ mol–1. The dynamical diameter of H2 molecules varies from 2.08 Å at 250 K to 1.64 Å at 100 K, and the diffusion constant ranges from 0.16 ± 0.03 rad ps–1 at 100 K to 0.49 ± 0.03 rad ps–1 at 250 K. These results indicate that no diffusion between the cages is observed in the picosecond time scale.

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Numerous experimental and theoretical investigations have been devoted to the hydrogen bond in pure liquids and mixtures. Among the different theoretical approaches, molecular dynamics (MD) simulations are predominant in obtaining detailed information, on the molecular level, simultaneously on the structure and the dynamics. Water and methanol are the two most prominent hydrogen-bonded liquids, and they and their mixtures have consequently been the subject of many studies; we revisit here the problem of the mixtures. An important first step is to check whether a classical potential model, the components of which are deemed to be satisfactory for the pure liquids, is able to reproduce the known thermodynamic excess properties of the mixtures sufficiently well. We have used the available BJH (water) and PHH (methanol) flexible models because they are by construction mutually compatible and also well suited to study, in a second step, some dynamic property characteristic of hydrogen-bonded liquids. In this article we show that these models, after a slight reparametrization for use in NpT simulations, reproduce the essential features of the excess mixing and molar properties of water-methanol mixtures. Furthermore, in the pure liquids, the agreement of the radial distribution functions with experiment remains as satisfactory as before. Similarly, the translation self-diffusion coefficients D are modified by less than 10%. In the mixtures, they evolve nonmonotonously as a function of mole fraction.