ORIENTATION-DEPENDENT INTERFACE MOBILITIES IN A KINETIC MEAN-FIELD THEORY OF FREEZING AND MELTING

The microscopic dynamics of freezing and melting at the 100 and 111 su rfaces of a simple cubic crystal are examined. The kinetics are descri bed using coupled Landau-Ginzberg equations based on a mean field appr oximation of the face centered cubic lattice gas with nearest and next nearest neighbor interactions. Anomalous large structural fluctuation s are found at the equilibrium 100 surface, a result of the weak coupl ing between close packed 100 planes. This feature also gives rise to a large anisotropy in interface mobilities on freezing with the 100 sur face mobility vanishing unless fluctuations or longer range interactio ns are included. The interface mobilities during melting are found to be substantially larger than those found during freezing for both surf aces, a result attributed to the asymmetry between crystal and liquid in the free energy functional.