Polymorphism in simple liquids: a Gibbs ensemble Monte Carlo study.

We perform Gibbs ensemble Monte Carlo (GEMC) simulations of a one-component system of hard spheres with a repulsive shoulder and an attractive well. We show the existence of two distinct liquid-gas and liquid-liquid phase equilibria. The GEMC estimate of the critical parameters, as following from an interpolation of the binodal points, is only slightly influenced by finite size effects. The liquid-gas critical temperature and pressure are lower than those of the liquid-liquid phase separation. A discussion of our findings in comparison with those of previous numerical studies is also presented.