| We apply quantum chemical methods to the study of electron correlation effects on the band structure of oxide systems. Our approach is based on a quasiparticle picture and a local Hamiltonian formalism. As a first example we choose MgO, a relatively simple closed-shell ionic oxide. Using the so-called cluster-in-solid embedding technique recently developed in our laboratory, we investigate the role of various electron correlation effects in reducing the Hartree-Fock band gap and modifying the band widths. As a second example, we discuss the electronic structure of the copper oxide superconducting compounds. We focus on the role of the background antiferromagnetic lattice in renormalizing the effective quasiparticle hoppings. Such effects are not accessible by density-functional calculations. In particular, the nearest-neighbor hopping matrix elements are reduced by a factor of four. Our results can describe very well the dispersion observed by angle-resolved photoemission measurements. |
|