A first principles Hartree_Fock description of MnO at high pressures

First-principles periodic Hartree-Fock calculations of MnO are reported which suggest that the phase transition recently observed under shock compression at similar to 90 GPa is not a simple B1-to-B2 transition of the type observed in CaO and SrO. The insulating B1 phase, which is rhombohedrally distorted as a result of spin-lattice interaction, is predicted to persist up to the phase transition pressure. Calculated Hugoniot curves based on a ferromagnetic Fm3m structure, with and without the inclusion of a posteriori correlation corrections, and a rhombohedrally distorted AF(II) structure are in close agreement with earlier static compression data. Beyond this pressure, calculations suggest that the phase is either an insulating distorted B2 phase or a metallic B2 phase.