Properties of solvate shells and the mobility of ions, according to molecular dynamics data

Abstract

The solvate shells of an ion, its velocity autocorrelation function, and diffusion coefficient D are found, and the interrelations between them are analyzed. A single ion in the system of atoms of a liquid is considered a model system. The interaction between the ion and atoms of the liquid is described by polarization potential U(r); the interaction between atoms of the liquid alone is described by the Lennard–Jones potential. A classical molecular dynamics method is used. Five solvate shells around the ion are found, and the lifetimes of atoms on each shell are calculated. It is found that the velocity autocorrelation function is of a vibrating nature. The spectrum of the autocorrelator and the frequency of cluster vibrations in a linear approximation are compared. Dependences D on parameters of potential U(r) are found. No dependence D on the ion mass is found; this is explained by solvation. The Einstein–Stokes formula and the HSK approximation are used in discussing the results. It is shown that at small radii of the ion, dependence D on parameters U(r) is described by such a model. When the ion radius is increased, the deviation from this dependence and an increase in D are observed. The results are compared to experimental mobilities of O₂^- and Ar₂⁺ ions in liquid argon.