Ab initio calculations of the elastic properties of ferropericlase Mg1−xFexO (x≤0.25x≤0.25)

Ferropericlase Mg1−xFexO is believed to be the second most abundant mineral in the Earth’s mantle. Therefore, the electronic and elastic properties of ferropericlase are important for the understanding of the Earth’s interior. Ab initio   total energy calculations have been performed for Fe concentrations x≤0.25x≤0.25. The equation of state (EOS) clearly shows a volume expansion as a function of Fe concentration, consistent with experimental data. Magnetic moment calculations as a function of pressure show a high-spin to low-spin transition of Fe2+, and the theoretical transition pressure increases with iron composition. At ambient pressure, we have found that the shear constant C44C44 reproduces well the experimental data as a function of Fe concentration. The MgO and Mg0.9Fe0.1O minerals show an increasing C44C44 with pressure, whereas the ΔC44/ΔP is slightly negative after 26 GPa for Mg0.8Fe0.2O. The C44C44 softening could be related to the transition from the cubic to a rhombohedrally distorted phase, recently found by experiment.