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

TL;DR

This study uses ab initio simulations and diagnostic plots to evaluate the equations of state for magnesium perovskite and postperovskite, highlighting the Vinet model's suitability over the Birch-Murnaghan model.

Contribution

It introduces a purely numerical diagnostic approach to assess equations of state, demonstrating the Vinet model's effectiveness for these minerals.

Findings

Vinet model provides consistent estimations of bulk modulus.

Discrepancies in previous studies are due to inappropriate equation choices.

The diagnostic approach clarifies the suitability of equations of state for geophysical minerals.

Abstract

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.