Application of the molecular dynamics method to a liquid system with long range forces (Molten NaCl)

Abstract

A significant and characteristic difficulty arising in the use of statistical mechanics to describe the properties of fused salts is due to the extreme range of the electrostatic field; an accurate representation of the Coulomb energy and Coulomb forces may be obtained using Ewald's expansion. Such calculations are tested here on the model case of liquid NaCl at different temperatures. In addition, this method is applied to the description of ionic media by molecular dynamics computations. (A Born-Huggins-Mayer pair potential is used with constants derived from the solid at 298 K.) This treatment introduces cut-off distances and periodic boundary conditions. The influence of these constraints on the conservation of energy and momenta is investigated. Thermodynamic properties of molten NaCl at 1164·5, 1224·5 and 1340·5 K are calculated. The motions of individual ions, anions and cations are described in terms of a velocity self-correlation function and their diffusion coefficients are determined.