Vapor-liquid equilibria of square-well spheres

Results of molecular dynamics (MD) simulations on square-well fluids with l ambda=1.25, 1.375, 1.5, 1.75, and 2.0 are presented. The calculation of vap or-liquid equilibrium was performed by isochoric integration of the liquid NVE data to obtain the free energy of the liquid and equating this to the v apor free energy from a modified virial equation. The saturation pressure w as investigated and compared with that from Monte Carlo simulation and seco nd-order analytical perturbation theory. The vapor pressures from the isoch oric integration technique are shown to be smoother than previous results, permitting accurate estimation of the effect of the square-well width on ac entric factor. With the saturated properties from molecular dynamics, the f value used in Kofke's Gibbs-Duhem integration was calculated and was found to be nearly constant. The related integration of the Clapeyron equation w as implemented as a check on thermodynamic consistency. Vapor pressures pre sented here are consistent to within 2%. (C) 1999 American Institute of Phy sics. [S0021-9606(99)51106-9].