Theoretical study of the stability of MgSiO3-perovskite in the deep mantle

We have used theoretical methods (Full-Potential Linear-muffin-tin-orbital, FPLMTO, and lattice dynamics) to calculate the Gibbs free energy of the ph ases, perovskite (MgSiO3), SBAD (SiO2), stishovite (SiO2) and periclase (Mg O). At 300 K, perovskite is found to be stable at all pressures up to 150 G Pa. As the temperature is increased, the free energy difference between the oxide mixture and perovskite decreases and at 3000 K and at pressures betw een 105 and 115 GPa, the oxide mixture becomes more stable. The calculated equilibrium pressure is much higher than the observed experimental pressure which may be due to stress in the sample and/or due to the inadequacy of t he applied theoretical models not accounting for anharmonicity effects.