No abstract

The itinerant LCAO picture based on localized atomic-like orbitals has been used to study the electronic ground state of NiO. The U-corrected local spin-density approximation (LSDA+U) yields energy-dispersion curves which show satisfactory agreement with the angular photoemission measurements. As a result the d states appear as narrow and well identified bands located above the 2p oxygen bands. The on-site Coulomb energy U increases the 2p character within the upper d valence band but not to the extent that NiO can be considered as a charge-transfer insulator.

The behavior of the 2p functions is studied in NiO within the local spin density approximation (LSDA) based on an LCAO representation. The ionicity is related to the spatial extension of the 2p orbitals and increases when the oxygen orbitals spread out. The corrected LSDA + U version enhances both the ionicity and the spin moment. As a result the intrasite Coulomb interaction U shrinks the d orbitals and extends the 2p functions.