Shell and breathing shell model calculations for isothermal bulk modulus in MgO at high pressures and temperatures

摘要

The constant temperature and pressure molecular dynamics (MD) have been performed to investigate the isothermal bulk modulus of MgO under high pressures and temperatures, using the shell model (SM) potential functions consisted of the Coulomb, dispersion, and repulsion interactions. 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 isothermal bulk modulus K_T of MgO dependence of the compression ratio V/V_0 and the pressure P have been obtained from MD runs at T=300 and 2000K, and compared with the available theoretical results. Compared with SM potential of Stoneham and Sangster [Phil. Mag. B 52 (1985) 717], the MD results with potential of Lewis and Catlow (LC) [J. Phys. C 18 (1985) 1149] are found to be in good agreement with the studies based on ab initio calculations, and the results obtained using BSM potential are more compressible. Meanwhile, K_T dependence of temperature T at zero pressure is investigated. At an extended pressure and temperature ranges, K_T has also been predicted. The properties of MgO are summarized in the pressure 0-200 GPa ranges and the temperature up to 3500 K.