Molecular dynamics simulations of the liquid-vapor interface of a molten salt. I. Influence of the interaction potential

Molecular dynamics simulations are used to calculate the surface tension gamma and study the structural properties of the liquid-vapor interface of the simple molten salt KI. The focus of the present paper is the effect on the calculated surface tension of different terms in the interionic potential and of the way that long-ranged interactions are treated. Specifically, we analyze the dependence of gamma on: (a) boundary conditions employed in the Ewald summations of Coulomb interactions; (b) truncation of dispersion interactions; (c) inclusion of polarization effects. Our results show that (a) the use of vacuum boundary conditions in the direction perpendicular to the interface helps to maintain the mechanical equilibrium of the interface; (b) an Ewald summation of dispersion interactions is necessary to avoid substantial truncation effects; (c) polarization tends to decrease gamma by significant amounts, and improves the agreement with experiment. In all cases, a reduction of gamma comes with a corresponding increase of the interfacial width. As a structural indicator, the tangential pair distribution functions at the interface are compared with those of the bulk liquid. (C) 2001 American Institute of Physics.