Nonperturbative density functional theory of solid-to-solid isostructural transitions

Abstract

We examine the phase diagram of systems of hard, spherical particles with a short-range attraction. Recent simulations as well as theoretical investigations predict for such systems an fcc-to-fcc isostructural transition which terminates at a critical point, and the existence of a single fluid phase. We use a nonperturbative density functional approach, by making a mapping of the inhomogeneous system onto a uniform fluid by means of the modified weighted density approximation (MWDA). Previous approaches were instead based on the separation of the potential into a hard-sphere repulsion and a short-range attraction with the latter treated in a mean-field fashion. We obtain improved results for the critical temperature, the middle density at the triple point and the overall shape of the phase diagram, but a worsening of the triple temperature with increasing range of interaction.