Molecular Dynamics Investigation of Homogeneous Nucleation in the Freezing of Selenium Hexafluoride

Simulations of phase changes provide a way to investigate nucleation at a depth of supercooling so far not accessible to laboratory experiments. One helpful aspect of this regime is that deficiencies of theory are substantially magnified, helping to call attention to the weaknesses of existing treatments. In the present molecular dynamics simulations, a system of small liquid clusters of SeF6 spontaneously froze to single body-centered cubic (bcc) crystals when cooled to 120 K. The transition was mediated by homogeneous nucleation rather than by spinodal decomposition. Its nucleation rate of 6.6 × 1035 m-3 s-1 was analyzed in both terms of classical nucleation theory (to derive the interfacial free-energy parameter) and Granasy's diffuse-interface theory (to derive the interface thickness parameter). In each case, both the classical prefactor and the Grant−Gunton (GG) prefactor were applied. Large differences between the various treatments were found. Derived interfacial free energies of 13−17 mJ/m2 were ...