High-pressure phase diagram of the exp-6 model: The case of Xenon

We investigated numerically the high-temperature/high-pressure phase diagram of Xenon as modelled through the Buckingham, exp-6 potential. This model is thought to provide an accurate description of the thermal behaviour of rare gases under extreme conditions. We performed a series of extensive Monte Carlo simulations which, in conjunction with exact computation of solid free energies by the Frenkel-Ladd method, allowed us to precisely locate the transition thresholds at various temperatures. We find that, upon isothermal compression, the exp-6 fluid freezes directly into a FCC solid; however, above 4500 K, an intermediate BCC phase may become stable in a very narrow range of pressures. We discuss these results in the light of previous numerical studies of the same model system and of the experimental data available for Xenon.