Comparative investigations of the P-V-T relationship of MgO with shell and breathing shell model molecular dynamics simulations

Molecular dynamics (MD) simulations have been performed to investigate the pressure-volume-temperature (P-V-T) relationship of MgO under high pressures and temperatures using the very similar shell model (SM) potentials with those of Stoneham and Sangster (SS) [Philos. Mag. B 52 (1985) 717] and Lewis and Catlow (LC) [J. Phys. C 18 (1985) 1149]. In order to take account of non-central forces in crystals, the breathing shell model (BSM) is also introduced in MD simulation, in which the repulsive radii of oxygen ions are allowed to deform isotropically under the effects of other ions in the crystal, with each core and breathing shell being linked by a harmonic spring with force constant k. The lattice parameter a, thermoelastic parameter αKT, and P-V relationship under different isotherms at selected temperatures and T-V relationship at zero pressure, have been obtained and compared with the available experimental data and other theoretical results. Compared with SM-SS and SM-LC potentials, the MD simulation with BSM is very successful in reproducing accurately the measured volumes of MgO. At an extended pressure and temperature ranges, P-V-T relationship has also been predicted. The properties of MgO are summarized in the pressure range of 0-2000 kbar and the temperature up to 5000 K.