Progression of phase behavior for a sequence of model core-softened potentials

A series of phase diagrams is obtained in three dimensions for a smooth pair potential with an outer well and a repulsive inner shoulder. Condensed phase boundaries are located using free energy calculations. Liquid-vapor equilibria are obtained with multicanonical methods. As the depth of the outer well is increased, a simple-hexagonal to close-packed transition appears in the solid, leading to a discontinuity in the slope of the melting curve. For deeper wells the simple hexagonal melting temperature exhibits a maximum with respect to pressure. The onset of the predicted metastable isostructural transition is also studied.