Orthobaric Densities from Simulations of the Liquid Vapour Interface

Abstract

Molecular dynamics studies of the liquid vapour interface of a Lennard-Jones fluid performed on a CYBER 205 are reported for kT/ε = 0.70, 0.85, and 1.10. The main emphasis is on the orthobaric fluid densities: their dependence on different cut-off radii and long range corrections as well as their comparison with the coexisting densities from bulk fluid simulations. As previously reported bubble densities from bulk simulations differ by about 3 per cent at kT/ε = 1.10, phase equilibrium was redetermined there with the NpT + test particle method. Concerning the bubble densities from the interface simulations, increase of the cut-off radius and use of long range corrections shift them up rather close to the “bulk” values. The dew densities from the interface simulations which for the usual cut-off radius of 2.5 [sgrave] are mostly too high by a factor of 3 are decreased dramatically by accounting for the long range part of the potential. For a cut-off radius of 5 [sgrave] and long range corrections they agree with the “bulk” values within the accuracy of the latters which, however, is estimated to be only by about 20 per cent. Some characteristic density profiles are also shown.

Key Words:

• Phase equilibrium
• liquid-vapour interface