The zero temperature Mott transition region in antiferromagnetic, spin S=5/2 MnO is probed using the correlated band theory LSDA+U method. The first transition encountered is an insulator-insulator volume collapse within the rocksalt structure that is characterized by an unexpected Hund's rule violating `spin-flip' moment collapse. This spin-flip to S=1/2 takes fullest advantage of the anisotropy of the Coulomb repulsion, allowing gain in the kinetic energy (which increases with decreasing volume) while retaining a sizable amount of the magnetic exchange energy. While transition pressures vary with the interaction strength, the spin-flip state is robust over a range of interaction strengths and for both B1 and B8 structures.
@article{arxiv.0803.3026,
title = {Pressure-driven magnetic moment collapse in the ground state of MnO},
author = {Deepa Kasinathan and K. Koepernik and W. E. Pickett},
journal= {arXiv preprint arXiv:0803.3026},
year = {2008}
}