Isostructural solid - solid transitions in square-shoulder systems

Applying a practical density-functional-based perturbation theory, we examine the phase behaviour of a model system interacting via a hard core plus a square-shoulder repulsion. For sufficiently narrow shoulders, the theory predicts coexistence between expanded and condensed isostructural (fcc) crystals, in quantitative agreement with available simulation data. In contrast to the attractive square-well system, atomic localization is found to increase with increasing temperature.