The melting of MgO - Computer calculations via molecular dynamics

Computer calculations based upon molecular dynamics have enabled us to model the melting behaviour of MgO, a significant component of the Earth's lower mantle. We have successfully employed the supercell method to study the mechanisms governing the melting process at ambient pressure, and this has enabled us to quantitatively predict values for melting temperature as a function of pressure in the range 0-150 GPa. We have performed melting calculations on a constant stress system containing 1728 inn nine a variety of potential models, all of which give a good description of the ambient structural, elastic and defect properties of our system. Our results show that the melting temperature of MgO rises from 2900-3400 K at zero pressure to similar to 8000 K at 150 GPa depending upon the potential model used. Our zero pressure results are comparable with previous calculations and close to the experimental value for zero pressure MgO melting of similar to 3100 K. We also calculate the melting volume and melting entropy of the system and find our results comparable with zero pressure experimental data for alkali halides but not with the recent high pressure results of Zerr and Boehler (1994) on MgO; the possible sources of this discrepancy are discussed.