  We investigated numerically the high-temperature/high-pressure phase diagram
of Xenon as modelled through the exp-6 interaction potential, which is thought
to provide a reliable description of the thermal behaviour of rare gases under
extreme conditions. We performed a series of extensive NVT Monte Carlo
simulations which, in conjunction with exact computation of the solid free
energy by the Frenkel-Ladd method, allowed us to precisely locate the freezing
and the melting thresholds at each temperature. We find that, under isothermal
compression, the exp-6 fluid freezes directly into a FCC solid; however, above
4500 K, an intermediate BCC phase becomes stable in a narrow range of
pressures. The chemical potential of the HCP phase does never significantly
differ from that of the FCC solid of equal T and P, though the former is found
to slightly overcome the latter. We discuss our results in the light of
previous numerical studies of the same model system and of the experimental
data available for Xenon.
