PERTURBATION WEIGHTED-DENSITY APPROXIMATION - THE PHASE-DIAGRAM OF A LENNARD-JONES SYSTEM

We present a density-functional approach for the Helmholtz free energy of simple liquids, based on the separation of attractive and repulsiv e interactions and within the framework of the weighted-density approx imations. The approach reduces to the standard perturbation theory of simple fluids for the homogeneous vapor and liquid phases. It gives a good description of the correlation structure in the crystal, based on a local-compressibility equation. The phase diagram of a Lennard-Jone s system is obtained and compared with a computer simulation.