First principle calculations of iron phosphide state equations at high temperatures and pressures of the Earth’s core

Abstract

In this article, the equations of state of iron phosphides Fe 2 P and Fe 3 P at high pressures and temperatures corresponding to P-T parmeters of the Earth’s inner core were studied using computer modeling methods based on the density functional theory. Two Fe 2 P structures with Pnma and P-62m symmetry and two Fe 3 P structures with I-4 and Cmcm symmetry are considered. The first-order phase transition pressures Fe 2 P and Fe 3 P are established. For each crystal structure considered, 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 Fe 2 P and Fe 3 P. It was found that the Fe 2 P-Pnma and Fe 3 P-Cmcm phases are thermodynamically stable at the pressures of the Earth’s inner core