Anomalous phase behavior of a soft-repulsive potential with a strictly monotonic force

摘要

We study the phase behavior of a classical system of particles interactingthrough a strictly convex soft-repulsive potential which, at variance with thepairwise softened repulsions considered so far in the literature, lacks aregion of downward or zero curvature. Nonetheless, such interaction ischaracterized by two length scales, owing to the presence of a range ofinterparticle distances where the repulsive force increases, for decreasingdistance, much more slowly than in the adjacent regions. We investigate, usingextensive Monte Carlo simulations combined with accurate free-energycalculations, the phase diagram of the system under consideration. We find thatthe model exhibits a fluid-solid coexistence line with multiple re-entrantregions, an extremely rich solid polymorphism with solid-solid transitions, andwater-like anomalies. In spite of the isotropic nature of the interparticlepotential, we find that, among the crystal structures in which the system canexist, there are also a number of non-Bravais lattices, such as cI16 anddiamond.