Effect of triplet correlations on the adsorption of a dense fluid onto a crystalline surface

Abstract

The adsorption of a fluid of hard spheres of diameter σ onto a planar surface containing a triangular lattice of adsorption sites, spacing σ, was studied using a model which is equivalent to a lattice gas with n-body interactions that are related to the n-body correlation functions of the fluid. The present paper extends our previous work, which included only pairwise interactions, to also include triplet interactions. We discovered a simple but accurate analytical approximation to the triplet correlation function for three spheres in mutual contact, which, when combined with a Müller–Hartmann and Zittarz approximation of the critical point in the equivalent lattice gas, yields the estimate ρcσ 3=0.8409 of the fluid density at the critical point of the condensation transition which occurs at the fluid–crystal interface. This estimate, which includes the effects of both pair and triplet correlations in the fluid, is significantly higher than the value ρcσ 3=0.6678 obtained if only the effects of pair correlations are included in the calculation.