The experimental values of the ratio of the radial seismic velocity perturbation with respect to the radial density perturbation, (R)T, for MgO at pressures of up to about 20 GPa show a conflicting pressure dependence. However, (R)T, calculated using free energy minimization at 1000 K and pressures of up to 160 GPa for the lower mantle minerals MgO and MgSiO3-perovskite, is predicted to decrease with increasing pressure. Previous calculations of the elastic constants of MgO using the Potential Induced Breathing model also predict that (R)T decreases as the pressure increases.

The ratio (dln&ngr;S/dln&ngr;@dP)T for both MgO and MgSiO3-perovskite is also predicted to decrease with increasing pressure.