Generalisation of the density-functional theory and three-body interactions in classical fluids

Abstract

An external field coupled with the two-body density distribution function leads to a generalisation of the density-functional theory in which the free energy is regarded as a functional not only of the density but also of the two-body distribution function. The generalised formalism is applied to the liquid structure theory in the presence of a weak three-body potential. The first-order calculation shows that the three-body effects are fully incorporated into the theory through modification of the pair potential by virtue of the variational property of the free-energy functional.