Phase relations in iron monoxides from LDA + Usc calculations

Wednesday, 16 December 2020
Yang Sun, Columbia University of New York, Earth and Environmental Sciences, New York, NY, United States, Matteo Cococcioni, University of Pavia, Department of Physics, Pavia, Italy and Renata Wentzcovitch, Columbia University in the City of New York, Department of Applied Physics and Applied Mathematics, New York, NY, United States
Understanding the pressure-dependent evolution of Earth forming phases containing iron is a challenging problem given the strongly correlated nature of iron oxides. Using the LDA+Usc method, we present calculation phase relations of iron monoxides involving five polytypes in multiple spin-state configurations. The Hubbard parameter U is determined self-consistently simultaneously with the occupation matrix and structures at arbitrary pressures. The Hubbard parameter strongly depends on pressure, structure, and spin state. Comparison with experimental structural data indicates the LDA+Usc can predict structure, compression curves, phase relations, and transition pressures very well for the insulating B1 and iB8 states. However, it requires additional calculations using the Mermin functional that includes the electronic entropic contribution to the free energy to obtain an nB8 metallic state and a consistent iB8 to nB8 insulator to metal transition pressure.

Research supported by NSF grant EAR-1918126