MODEL FOR DENSITY-FUNCTIONAL THERMODYNAMIC PERTURBATION ANALYSIS OF LENNARD-JONES SOLIDS

Thermodynamic perturbation theory and density-functional approximations are systematically combined to produce a model of Lennard-Jones solids and solid-liquid coexistence. The perturbation theory is based on expanding the free energy about that of the fcc hard-sphere solid, which is described by an accurate nonperturbative density-functional theory. Approximations made throughout the development are systematically checked against results of Monte Carlo simulations. The Gaussian approximation used for describing the solid density is shown to be a good approximation for the stable solid; however, anisotropies in the structure that are not captured by the Gaussian approximation become pronounced at densities corresponding to metastable solids. The free energies of both the solid and the liquid Lennard-Jones phases and the phase diagram predicted by the density-functional thermodynamic perturbation model are in good agreement with Monte Carlo simulations for temperatures in the range 0.75 less-than-or-equal-to kT/epsilon less-than-or-equal-to 100.