Phase diagram of the Weeks-Chandler-Andersen potential from very low to high temperatures and pressures

Abstract

A combination of two molecular simulation algorithms has been used to determine the solid-liquid coexistence of the Weeks-Chandler-Andersen (WCA) fluid from low temperatures up to very high temperatures. Values are reported for the coexistence pressure, temperature, energy, enthalpy change, and densities of both the liquid and solid phases. At very high temperatures, the coexistence pressure approaches the same 12th-power soft-sphere asymptote as the 12-6 Lennard-Jones potential. However, in contrast to the Lennard-Jones potential, which shows a discontinuity of pressure at low temperatures, the coexistence pressure of the WCA potential approaches the zero-temperature limit. Empirical relationships are determined to accurately reproduce the coexistence pressure and both solid and liquid phase densities from near zero temperature to very high temperatures. The simulation data are used to improve the accuracy of a WCA equation of state. The validity of common melting and freezing rules is tested.