Detailed study of potassium solvation using molecular dynamics techniques

Molecular dynamics simulations are carried out to examine the solvation pro perties and the ion-solvation shell exchange process of the K+ ion in liqui d water; chloroform, and carbon tetrachloride. The solvent molecules are fo und to form well-defined solvation shells around the K+ ion and show a pref erred orientational order toward the ion. The induced dipole moment distrib ution of K+ becomes broader and shifts to a larger average value from chlor oform to carbon tetrachloride to water. It is observed that the K+ ion diff uses more rapidly in the aqueous phase than in liquid chloroform and carbon tetrachloride. We have also evaluated both ion and first solvent shell vel ocity autocorrelation functions and the residence time autocorrelation func tions for the ion in water, chloroform, and carbon tetrachloride. The resid ence time is found to be 9.4 ps for water and about 30 ps for both chlorofo rm and carbon tetrachloride. By use of a constrained molecular dynamics tec hnique,: 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 dissoci ation rates.