The melting of CaF2 and its (110) surface structure investigated by molecular dynamics simulation

Classical molecular dynamics using rigid-ion and shell-model potentials has been used to investigate the high-temperature properties of the (110) surface of CaF2. The rigid-ion model generates missing-row defects well below the melting point, giving alternate (111), (111) and (110) microfacets along the [001] direction. Simulations of about 1 ns duration are necessary to establish these surface structures. It is suggested that ultimately this process would result in the formation of extended (111) facets in a larger system than those studied here. Shell-model simulations, which were necessarily shorter than their rigid-ion counterparts, did not produce these structures. However, the inclusion of polarizability markedly increases the rate of F− superionic diffusion at a given temperature, and of cation and anion diffusion in the melt. It also results in a reduction of about 15% in the melting point compared with the rigid-ion model.