Electronic Structure of the $3d$ Transition-Metal Monoxides. I. Energy-Band Results

The augmented-plane-wave (APW) method is applied to calculate the nonmagnetic band structures for the $3d$ transition-series monoxides CaO, TiO, VO, MnO, FeO, CoO, and NiO, all of which form with the rocksalt structure. The APW energy-band results at seven symmetry points in the fcc Brillouin zone are fitted with the Slater and Koster linear-combination-of-atomic-orbitals (LCAO) interpolation method involving nonorthogonal orbitals. A nonlinear least-squares fitting procedure is applied to determine 16 two-center energy and overlap LCAO parameters which characterize the oxygen $2s-2p$ and transition-metal $3d$ energy bands and their interactions. It is found that both the APW results and the corresponding LCAO parameters exhibit systematic variations across this series of compounds. These calculations predict that: (a) CaO is an insulator with a 10-eV band gap; (b) the metallic oxides TiO and VO have $3d$ bandwidths of about 0.5 Ry, which are two and a half times larger than those for the antiferromagnetic insulators MnO, FeO, CoO, and NiO; (c) the energy of the $3d$ band decreases systematically (relative to the bottom of the transition-metal $4s-4p$ band) as the nuclear charge is increased, causing the metal $s-d$ bands to overlap for the early but not the later members of this series.