Equations of state of magnesium perovskite and postperovskite: diagnostics from ab initio simulations

The isothermal compression of magnesium perovskite and postperovskite is examined through the F-f plot and the diagnostic plot of Vinet universal model theoretically from the ab initio quantum-mechanical calculations at the hybrid Hartree-Fock / Density Functional Theory level. A purely numerical approach, first time applied in this paper, shows that the discrepancies largely observed between studies on the perovskite and criticized in geophysical applications are due to the inadequate choice of the Birch-Murnaghan equation of state; meanwhile the Vinet model is found utterly appropriate for the mineral and infers consistent estimations of the bulk modulus and its pressure derivative. The diagnostics of the postperovskite suggest similar conclusions.