Hybrid density functional study of Mott transition in MnO

The electronic structure, the magnetic moment and volume collapse of MnO under pressure is obtained from hybrid density functional theory using the recently developed screened hybrid exchange-correlation functional of Heyd, Scuseria and Ernzerhof (HSE). We study two crystal structures for MnO: cubic (rock salt) and hexagonal (nickel arsenide). We find two antiferromagnetic states for the NaCl structure: a high-spin state that couples two $S=5/2$ moments, and a low-spin state that couples two $S=1/2$ moments. At ambient pressure the high-spin state lies lowest. The low-spin phase becomes favored at a pressure of about $248\,\mathrm{GPa}$, leading to a first order volume collapse. However, this transition is pre-empted by another first-order volume collapse at $178\,\mathrm{GPa}$ from the NaCl structure to a NiAs structure. This transition is predicted to be insulator to metal and is the realization of the Mott transition.