Classical multicomponent fluid structure near solid substrates: Born-Green-Yvon equation versus density-functional theory

Abstract

We report a study of adsorption of binary mixtures of hard spheres of different sizes on a hard wall by using a version of density-functional theory, the Born-Green-Yvon (BGY) equation and Monte Carlo simulations. Following the BGY approach introduced by Fischer and Methfessel for single-component fluids, the proposed extension uses coarse-grained densities to approximate the contact values of pair distribution function of hard spheres. A procedure for evaluation of the coarse-grained densities, leading to an exact theory in one dimension, is proposed. The density-functional theory employed here, however, uses the Meister-Kroll and Groot approach. Comparisons of theoretical calculations with Monte Carlo simulations, as well as with previous theoretical predictions, have shown that density-functional theory reproduces the pseudo-experimental data accurately, even for extremely large size ratios of molecules of both species. The accuracy of the predictions of the BGY approach is less satisfactory, and for h...