The direct correlation function in hard sphere fluids

Abstract
The pair correlation function in a homogeneous hard sphere fluid at various densities has been measured in a large system, using the Monte Carlo method. The corresponding direct correlation function C2(r) has been determined directly from these measurements, and will be given here in closed form. We conclude that density functional models that neglect the effect of C3 and higher order direct correlation functions, that are defined in bulk fluids, are not able to describe an inhomogeneous hard sphere fluid accurately.