EFFECTS OF PRESSURE ON DIFFUSION AND VACANCY FORMATION IN MGO FROM NONEMPIRICAL FREE-ENERGY INTEGRATIONS

The free energies of vacancy pair formation and migration in MgO were computed via molecular dynamics using free-energy integrations and a n onempirical ionic model with no adjustable parameters. The intrinsic d iffusion constant for MgO was obtained at pressures from 0 to 140 GPa and temperatures from 1000 to 5000 K. Excellent agreement was found wi th the zero pressure diffusion data within experimental error. The hom ologous temperature model which relates diffusion to the melting curve describes well our high pressure results within our theoretical frame work. [S0031-9007(97)04344-5].