Generalized van der waals theory of interfaces in simple fluid mixtures

An efficient implementation of the generalized van der Waals theory of flui ds is presented for the calculation of surface tension in simple fluid mixt ures. While detailed correlation analysis is avoided the dominant binding e nergy contribution and the negative contribution due to the nonlocal entrop y are accounted for in the free energy density functional by simple physica l approximations of the type originally introduced by van der Waals, Effici ent computation is achieved by the use of a single-parameter optimization o f a tanh-shaped profile representing the total density as well as the compo sition variation across the interface. This simple profile nevertheless inc orporates the expected adsorption to the interface of the volatile componen t. Application is made to argon/krypton mixtures represented by Lennard-Jon es potentials and Lorentz-Berthelot combining rules. Surface tension predic tions compare well with both experimental observations and computer simulat ion results which also indicated close agreement in particle density profil es, especially if the Berthelot rule is amended with a binary interaction p arameter slightly (3%) less than unity. (C) 2001 Academic Press.