Detailed study of potassium solvation using molecular dynamics techniques

Molecular dynamics simulations are carried out to examine the solvation properties and the ion-solvation shell exchange process of the K+ ion in liquid water; chloroform, and carbon tetrachloride. The solvent molecules are found to form well-defined solvation shells around the K+ ion and show a preferred orientational order toward the ion. The induced dipole moment distribution of K+ becomes broader and shifts to a larger average value from chloroform to carbon tetrachloride to water. It is observed that the K+ ion diffuses more rapidly in the aqueous phase than in liquid chloroform and carbon tetrachloride. We have also evaluated both ion and first solvent shell velocity autocorrelation functions and the residence time autocorrelation functions for the ion in water, chloroform, and carbon tetrachloride. The residence time is found to be 9.4 ps for water and about 30 ps for both chloroform and carbon tetrachloride. By use of a constrained molecular dynamics technique,: the first solvation shell exchange process is investigated. It is found that an estimate using equilibrium solvation and classical transition-state theory overestimates the dissociation rate of the K+ ion. Including the dynamical effects using Grote-Hynes theory yields more accurate dissociation rates.