Phase behavior of aligned dipolar hard spheres: integral equations and density functional results

Using reference hypernetted chain integral equations, we investigate the phase behavior of a system of dipolar hard spheres with perfect orientational order. At low densities, the correlation functions show a strong tendency to the formation of head-to-tail chains. The occurrence of a condensation of the chains, as suggested by a recent simulation, is critically discussed. At higher densities the structure of the liquid phase already reflects well defined positions of the chains relative to each other, similar to a body-centered-tetragonal structure. Minimizing a density functional of the grand canonical free energy which is based on the liquid correlation functions, we calculate the coexistence lines at freezing. Interestingly, the system freezes at much lower temperatures than the corresponding isotropic fluid.