Crystal stability of heavy-rare-gas solids on the melting line

Contrary to static-energy predictions favoring a hexagonal-close-packed phase, heavy rare gases solidify into a face-centered-cubic phase over a large temperature range. Our recent perturbation theory and hard-sphere radial distribution functions are applied to give a conclusive calculation that agrees with experiment near the melting lines of heavy-rare-gas solids. The observed stability is due to thermal contributions to the Helmholtz free energy which far exceed the opposing static term. The Lennard-Jones potentials used here reproduce melting data of these solids to 1 GPa.