A validity test of the WCA perturbation theory for two-dimensional Lennard-Jones fluids

Abstract

The potential energy and pressure are obtained from molecular dynamics simulations of two-dimensional Lennard-Jones fluids over a wide range of densities and temperatures, thus testing the validity of first-order (high temperature approximation) and second-order Weeks-Chandler-Andersen theory. The pressure results, which are very important for a subsequent analysis of adsorption theories, are very much affected by that approximation, especially at low densities and, surprisingly, at very high densities. For the potential energy the effect is smaller, and the approximation gives good results at intermediate and high densities even at low temperatures. The conclusion is that the second-order term of the Weeks-Chandler-Andersen theory is needed for theoretical calculations of the pressure, except at very high temperatures and intermediate densities. Nevertheless, the first-order term gives good results for the potential energy except at low densities. All these findings are necessary for a complete analysis of the validity of the Weeks-Chandler-Andersen theory and its consequences in the study of the adsorption of rare gases onto flat surfaces.