Mass effects and transport properties in classical fluids: A molecular dynamics experiment on fused NaCl

Abstract

The mass dependence of the ionic transport properties has been studied by molecular dynamics calculations on a model of liquid NaCl. It is shown that changes in the mass of one set of constituent particles (cation or anion) have a similar influence on the motion of all particles. Moreover, the change in transport and relaxation coefficients due to isotope substitution in the absence of quantal effects is very small, in contrast with the situation observed in gases and ionic solids.

The mean square displacements and the velocity autocorrelation functions are computed in order to evaluate quantitatively the time evolution of the mass effect. An expansion in powers of the mass difference (with respect to a reference system) has been developed to describe the perturbation of the velocity correlation functions.