Crystallization mechanisms for supercooled liquid Xe at high pressure and temperature: Hybrid Monte Carlo molecular simulations

We report hybrid Monte Carlo molecular simulation results on the crystallization of supercooled liquids of xenon at high temperature and high pressure. We simulate the entire crystallization process, i.e., the nucleation event as well as the subsequent growth of the critical nucleus, at P = 4.46 GPa and P = 87.96 GPa. In both cases, we carry out the simulations at a temperature 25% below the melting temperature. We demonstrate that the crystallization mechanism strongly depends on pressure. At P = 4.46 GPa, crystal nucleation and growth both proceed through the face centered cubic (fcc) polymorph. At P = 87.96 GPa, throughout nucleation and growth, the crystallites are always predominantly of the body centered cubic (bcc) form. However, at P = 87.96 GPa, our simulations reveal that the crystallization mechanism is rather complex. Precritical as well as large postcritical crystallites can often be described as composed of several blocks: a large block of the thermodynamically stable bcc polymorph and smaller metastable fcc blocks, which gradually convert into the stable bcc form. We rationalize these results in terms of the relative stability of the phases involved and compare the crystallization mechanism of xenon to those recently observed on model systems.