Density-functional theory of simple classical fluids. I. Surfaces

A density-functional theory appropriate to nonuniform simple classical fluids is developed. Unlike most previous theories, the theory is in principle exact in the linear-response regime. For practical applications a small number of well-defined approximations, including that of Percus and Yevick, are made. Given only the Lennard-Jones 6-12 potential as input, the theory yields surface tensions and profiles in very good agreement with the results of Monte Carlo calculations. For a liquid pressed against a hard wall the expected oscillations in density in the vicinity of the wall are obtained. Comparisons with previous theories are made, and points of possible improvement in the formalism are discussed.