Mean-field analysis of the three-band Hubbard model

A full three-band model for the CuO2 plane of cuprates, which includes all the essential interaction - Cu-O and O-O hopping and the Coulomb repulsion on the Cu and O sites and between them, is considered. Its antiferromagneti c ground state for the half-filling is studied by using the mean field appr oximation. The electronic structure and the magnetic properties such as the densities of states, the energy spectra, the composition of holes (Cu or O character), the superexchange interaction and the magnetic moment are calc ulated and in general, our results are in agreement with the available expe rimental and other calculation results. Meanwhile, we find that the influen ce of the O-O hopping and Cu-O intrasite Coulomb repulsion on these propert ies is considerable. Our estimate of the energy of the spin singlet state a bove the antiferromagnetic background indicates that the lowest excitation state of the holes is the singlet state and give a charge-transfer energy i n agreement with the experiment. We also discuss the hole-doping to the ant iferromagnetic background and find the mean field approach invalid. Finally , based on the electronic structure at the half-filling, en effective one-b and Hubbard model is presented and the effective parameters are close to th e values given by the computation on the clusters.