Solvent-averaged potentials for Na+-Cl-, Na+-Na+, and Cl--CI-in methanol have been evaluated using the constrained molecular dynamics simulation technique. Solvent contributions to the total force on the solute pairs have been analyzed carefully in all of the systems. In order to get a deeper insight into the influence of the solvent on the ion pairs, the most probable solvent distributions at the relevant points of the calculated mean force potentials have been studied. Our mean force potentials show important discrepancies with the ones obtained using the RISM (reference interaction site model) approximation. Friction kemels for the relative dynamics of the ion pairs have also been evaluated. The passage across the barrier existing in the Na+-Cl-mean-force potential has been analyzed in light of Kramers and Grote-Hynes theories. It tums out that the association-dissociation process takes place in the polarization caging regime. A comparison between our results and the ones corresponding to the same ion pairs in water has been done.

Molecular dynamics simulations of solutions made up by one ion in methanol have been performed. The ions under study have been Na ϩ and Cl Ϫ . Structural and dynamical data as well as the dynamics of solvation have been analyzed. Both translational and reorientational motions of solvent molecules have been studied. An analysis of the solvent response to instantaneous changes of the electrical distribution of the solute in the linear response approximation has been undertaken. Special attention has been paid to differences between solvent molecules in the first shell and in the bulk, which happen to be more important in the Na ϩ shell. The influence of the ionic mass on the solvent properties has also been studied.

Free energies of ion hydration have been evaluated by using the thermodynamic integration technique ͑the slow growth method͒ in molecular dynamics simulations. Ionization processes of Na, Ca, and Cl have been considered. The cutoff method and the Ewald summation approach have been used alternatively in truncating the long-range electrostatic interactions. The extended simple point charge ͑SPC/E͒ model ͓J. Phys. Chem. 91, 6269 ͑1987͔͒ and the ion-water potentials of Straatsma and Berendsen ͓J. Chem. Phys. 89, 5876 ͑1988͔͒ have been used in our simulations. The results have been tested against experimental measurements and the Ewald method has led to the best performances. A good agreement with the Born model was found in the charging process of a calcium ion. Changes in the organization of water molecules around the ion have been evaluated from equilibrium molecular dynamics simulations performed at different stages of this process. Ion-water radial distribution functions, and the orientation of water molecules as well as residence times have been analyzed.

Molecular dynamics calculations of molten salts and soft-sphere binary liquid mixtures have been performed. The self-and cross-correlations of the atomic velocities and displacements are studied from the corresponding time-correlation functions and diffusion coefficients. The effects of both the direct and hydrodynamic interactions on the dynamic cross-correlations as well as their dependence on the reference frame are discussed. The time cross-correlation functions resulting from stochastic simulations by the generalized Langevin dynamics method are also considered.

No abstract