Re-entrant melting of the exp-6 fluid: the role of the repulsion softness

We investigate the phase behaviour of a system of particles interacting through the exp-6 pair potential, an interaction model that is appropriate to describe effective interatomic forces under high compression. The softrepulsive component of the potential is being varied so as to study the effect on re-entrant melting and density anomaly. Upon increasing the repulsion softness, we find that the anomalous melting features persist and occur at lower pressures. Moreover, if we reduce the range of downward concavity in the potential by extending the hard core at the expenses of the soft repulsive shoulder, the re-entrant part of the melting line reduces in extent so as it does the region of density anomaly.