Ionic dynamics in the LiCl–KCl system at liquid state

Abstract

The mixing effects in the fused system LiCl–KCl are studied by molecular dynamics simulation. The predominant contribution of the Coulombic interaction is clearly detected, its nonlinear variation gives rise to the main part of the excess internal energy. This change reflects the structural ionic arrangement; at high potassium concentration a significant decrease of the Li+–Cl− distance is observed. The anion–cation radius ratio has a marked effect: the lithium ions remain fourfold coordinated by chloride ions throughout the concentration range while the potassium ions are about sixfold coordinated. It is shown that the ion motion proceeds from two main mechanisms: an oscillatory displacement in the force field of the surrounding particles which tends to restore the electroneutrality and a collective mode which concerns the ion and its ionic atmosphere. This approach is described by the generalized Langevin equation and may open a better understanding of the transport processes at liquid state. It provides a link between the structure and the dynamical properties, the strong Li+–CL− interactions leading to a significant decrease of the Li+ mobility when the potassium concentration increases.