Transition-Metal Monoxides: Band or Mott Insulators

We argue that the widely held view that MnO, FeO, CoO, and NiO are Mott insulators is incorrect. Intra-atomic potential energies do not dominate interatomic kinetic energies, to the extent commonly believed; both are 1-2 eV in magnitude. A measure of the importance of interatomic effects is our finding that both the crystal structure and the magnetic structure of these materials are crucial to their insulating behavior. © 1984 The American Physical Society.