Density Functional Theory and the Capillary Evaporation of a Liquid in a Slit

Abstract

Density functional theory is applied to a Lennard-Jones fluid near a single hard wall and in a slit formed by two walls. We use some simplified versions of the Weeks–Chandler–Andersen (WCA) and the Barker–Henderson (BH) theories. Only the most crude mean field version of the WCA theory, in which the hard-sphere correlation function is set equal to unity for all distances, seems useful. Use of the full WCA approximation is impractical because the effective hard-sphere diameter is density dependent. Generally, the best results are obtained using the BH macroscopic compressibility approximation. Our earlier study of “evaporation” of Lennard-Jones molecules in a slit is extended to other densities using the mean field theory.