The exp-6 potential fluid at very high pressures: computer simulations and theory

Abstract

The exp-6 potential fluids for four values of the softness parameter α, ranging from 11·5 to 14·5, have been investigated both by computer simulations and theory at supercritical temperatures and very high densities (pressures). Tables of the simulation data for pressure include altogether 141 thermodynamic state points generated at six temperatures for each α. In addition to computation of the thermodynamic properties, great attention has been paid to the structure, and an approximate location of the onset of freezing has been determined. To estimate the properties of the fluid from theory, a modified version of the Weeks–Chandler–Anderson (mWCA) theory and the optimized reference hypernetted chain (RHNC) theory were used. It is shown that for the thermodynamic properties mWCA theory performs very well under all stable fluid conditions considered, whereas RHNC theory, comparable with mWCA at the lower densities considered, gradually loses its accuracy in the very high density range. However, for structure the overall performance of RHNC theory is considerably better than that of mWCA, which points to possible cancellation of errors in the latter theory when applied to thermodynamic properties.