2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/171461We investigate the electronic states of the CoO_2 plane in the layered cobalt oxides Na_{0.5}CoO_{2} using the realistic 11 band d-p model on a two-dimensional triangular lattice. Effects of the Coulomb interaction on a Co site: the intra- and inter-orbital direct terms U and U', the exchange coupling J and the pair-transfer J', are treated within the Hartree-Fock approximation. It is found that the metallic antiferromagnetism takes place below T_{c1} and, in addition, the orbital order accompanied by the small charge order takes place below T_{c2} (< T_{c1}) where the system becomes insulator. The obtained results are consistent with the successive phase transitions observed in Na_{0.5}CoO_{2}.4 pages, 5 figuresStrongly Correlated Electronstext