First principle calculations of iron phosphide state equations at earth core pressures

Abstract

In this article, the equations of the state of iron phosphide at pressures corresponding to the conditions of the
earth’s core are studied using computer modeling methods. Two Fe 2 P structures of Pnma and P-62m symmetry and two Fe 3 P structures with I-4 and Cmcm lattice symmetry are considered. For each considered crystal lattice, the equation of state P(V) is constructed without taking into account thermal effects and pressures up to 200 GPA. Calculations of the equations of state
were carried out with and without taking into account the magnetic ordering in the considered compounds. It is shown that the magnetic order strongly affects the behavior of the P(V) functions in the low pressure region for Fe 2 P-Pnma and Fe 3 P-I-4 crystals. This dependence correlates well with the calculated dependence of the magnetic moment of the considered compounds as a function of pressure. The relative stability of the considered structures is also studied. It is shown that the Fe 2 P-Pnma
lattice is more stable over the entire range of the considered pressures in the limit of neglect of thermal effects. The Fe 3 P-I-4 structure is more stable in the low pressure region and the transition to the Fe 3 P-Cmcm phase occurs at a pressure of 25 GPA.