FLUID-PHASE EQUILIBRIA USING MOLECULAR-DYNAMICS - THE SURFACE-TENSIONOF CHLORINE AND HEXANE

In this paper we demonstrate that the direct molecular dynamics method can be used to predict accurate fluid phase equilibria for molecular fluids. The method is applied to chlorine and n-hexane to calculate th e coexisting densities, vapour pressure, and surface tension as a func tion of temperature. Chlorine is modelled as a rigid diatomic molecule , and n-hexane as an isotropic united-atom model. For hexane we use tw o sets of parameters for the intermolecular potential. The main differ ence in the parameters is the strength of the repulsion-dispersion int eraction of the terminal methyl group epsilon(CH3)/k = 90.44 K (model I) and = 114 K (model II); systematic differences in the calculated pr operties are found for the models. For chlorine, the liquid-vapour den sities and vapour pressures are in excellent agreement with experiment al results, and with those previously calculated using the Gibbs ensem ble Monte Carlo method (GEMC). Good agreement with the experimental su rface tensions is obtained. For hexane, the calculated properties are in better agreement with experiment for model I. The coexisting densit ies calculated in this work are in very good agreement with those calc ulated using the GEMC method.