N-band Hubbard models for copper oxides and isoelectronic systems. New models for organic and organometallic magnetic conductors and superconductors

The electronic structures of undoped and doped copper oxides and other related oxides are investigated on the basis of the N-band Hubbard models. The Hubbard Hamiltonians for clusters of transition metal oxides are exactly diagonalized by the full valence-bond (VB ) configuration interaction (CI) method in order to elucidate populations of doped holes, electronic excitation energies, etc. Possible mechanisms of the high-T_c superconductivity for oxide superconductors are discussed on the basis of the calculated results, together with available experiments. The analysis of correlation and spin correlation effects on doped copper oxides indicates theoretical possibilities of new models for organic and organometallic magnetic conductors and superconductors. Organic and organometallic analogs to copper oxides are therefore proposed on the basis of these results.