Is perturbation DFT approach applicable to purely repulsive fluids?

Abstract

A recently proposed third order + second order perturbation density functional theory (DFT) approach is tested for the validity and applicability to purely repulsive model fluids subjected to various external fields. Hard core repulsive Yukawa potential, point particle Yukawa potential, and inverse power potential are employed as sample models. Theoretical DFT results are compared with the corresponding simulation data obtained by grand canonical ensemble Monte Carlo simulation. This comparison indicates that the third order + second order perturbation DFT approach is suitable for these purely repulsive fluids only on condition of high accuracy of the imported bulk second order direct correlation function (DCF). However, in this case the origin of the successful performance somewhat differs from that observed for the mean field approximation applied to van der Waals fluids. In the present case it originates from the observation that the bulk second order DCF is strongly dependent on the density argument for the hard-core part, while for the distances exceeding the core dimension this dependence is considerably weaker.