Phase stability of wüstite at high pressure from first-principles linearized augmented plane-wave calculations

We use the local spin-density approximation (LSDA) to investigate the phase stability and physical properties of stoichiometric wüstite at high pressure. Highly converged total-energy calculations are presented for nonmagnetic, ferromagnetic, and antiferromagnetic, unstrained B1 and B2, and rhombohedrally strained B1 structures. We find the local magnetic moments are greatly diminished at high pressure, and we expect the LSDA to provide an accurate description of FeO at high pressure. The antiferromagnetic ground state occurs for a small rhombohedral distortion of the B1 structure. The rhombohedral angle α decreases with increasing pressure, in agreement with available x-ray data. Our results elucidate the phase relationship between the B1 and B2 structures of FeO, and explain why no transition has yet been observed in room-temperature static experiments up to 220 GPa, whereas a transition to a metallic, and possibly B2, phase has been observed at 70 GPa and high temperature. We predict that a transition to a metallic B2 structure will occur from a rhombohedrally strained B1metallic phase near 500 GPa, provided no further distortions to lower symmetry occur in the rhombohedral lattice.