The vapour-liquid interface for a Lennard-Jones model of argon-krypton mixtures

Abstract

We report a molecular dynamics study of the planar vapour-liquid interface for mixtures of Ar and Kr modelled by truncated Lennard-Jones potentials at 115·77 K and at two compositions. The simulations yield the density profiles, surface tension, surface of tension, adsorption, and normal and transverse components of the pressure tensor. Both the Irving-Kirkwood (IK) and Harasima (H) forms of the pressure tensor are calculated. The values of the surface tension calculated by the thermodynamic and mechanical (for both the IK and H pressure tensors) routes are in agreement, but the IK and H pressure tensors yield different values for the surface of tension, as expected. These results are compared with predictions of the mean field theory (MFT) of the interface. The agreement is generally good, the principal differences being due to the fact that the MFT predicts too low a liquid density. The MFT is also used to predict properties of the mixture interface for the full Lennard-Jones potential. For low concentrations of argon, the argon density profile is predicted to be weakly non-monotonic; this effect is larger for the full than for the truncated Lennard-Jones potential.