Perturbation density functional theory for nonuniform fluid mixture based on Lagrangian theorem

First order direct correlation function (DCF) of non-uniform fluid mixture was expanded around the bulk fluid mixture, the expansion was truncated at the lowest order and made formally exact by making use of functional counterpart of Lagrangian theorem of differential calculus. The concrete procedure involves the specification of the non-uniform component i-component j pair second order DCF by their respective uniform counterpart with appropriate weighted packing fraction and weighted concentration as their arguments. As an example, the truncated expansion was incorporated into the density functional theory (DFT) formalism to predict the density profile of binary hard sphere fluid near a structureless hard wall. Good agreement between theoretical predictions and simulation data demonstrates the reliable accuracy of the present approach. (C) 2003 Elsevier B.V. All rights reserved.