First principle calculations of iron phosphide state equations at high temperatures and pressures of the Earth’s core
In this article, the equations of state of iron phosphides Fe2P and Fe3P at high pressures and temperaturescorresponding to P-T parmeters of the Earth’s inner core were studied using computer modeling methods based on the densityfunctional theory. Two Fe2P structures with Pnma and P-62m symmetry and two Fe3P structures with I-4 and Cmcmsymmetry are considered. The ﬁrst -order phase transition pressures Fe2P and Fe3P are established. For each crystal structureconsidered, the equation of state P(V) is constructed using the lattice dynamics method in a quasi -harmonic approximation,taking into account thermal eﬀects up to a pressure of 400 GPA. Phonon dispersion curves were calculated for Fe2P and Fe3P.It was found that the Fe2P-Pnma and Fe3P-Cmcm phases are thermodynamically stable at the pressures of the Earth’s innercore.