First-principles study on electronic structures and phase stability of MnOand FeO under high pressure

The electronic structures and the phase stability of MnO and FeO under ultr ahigh pressure were studied by the first-principles plane-wave basis pseudo potential calculations. Different crystal structures combined with differen t spin structures were studied systematically for both MnO and FeO with ful l structure optimization. The present calculations based on generalized gra dient approximation (GGA) account well for the properties of MnO and FeO es pecially in the high-pressure region. For the low pressure regime, where th e electron correlation is very strong, we performed the LDA+U calculations with the electron correlation and the spin-orbit coupling taken into accoun t to supplement the GGA results. Our results predict that the high-pressure phase of MnO should take the metallic normal NiAs (nB8) structure rather t han the B2 structure, and that a metastable nonmagnetic B1 structure with s tretched distortion along the [111] direction can be realized for MnO in th e intermediate pressure range. A unique antiferromagnetic inverse NiAs (iB8 ) structure as the high-pressure phase of FeO was discussed in detail, and the uniqueness was made clearer by comparing with the FeS case. The distort ions and the magnetic moments for different phases were characterized. The larger cia ratios for both nB8 MnO and iB8 FeO can be explained based on ou r analysis of the cation-radius/anion-radius ratio versus cia for series of related materials. [S0163-1829(98)01246-6].