  Using the non-empirical Variational Induced Breathing (VIB) model, the
thermal properties of periclase (MgO) under high pressures and temperatures are
investigated using molecular dynamics, which includes all anharmonic effects.
Equations of state for temperatures up to 3000K and pressures up to 310 GPa
were calculated. Bulk modulus, thermal expansivity, Anderson-Gruneisen
parameter, thermal pressure, Gruneisen parameter and their pressure and
temperature dependencies are studied in order to better understand high
pressure effects on thermal properties. The results agree very well with
experiments and show that the thermal expansivity decreases with pressure up to
about 100 GPa ($\eta$=0.73), and is almost pressure and temperature independent
above this compression. It is also effected by anharmonicity at zero pressure
and temperatures above 2500K. The thermal pressure changes very little with
increasing pressures and temperatures, and the Gruneisen parameter is
temperature independent and decreases slightly with pressure.
