Approximate treatment of the three-band Hubbard model

An approximate treatment of the three-band Hubbard model is developed which allows the calculation of spectral functions on the CuO2 planes of superconducting cuprates. The lattice is divided into CuO2 clusters (trimers), on which the Hamiltonian can be diagonalized. The hole concentrations on both orbitals and the amplitude of the staggered magnetization are obtained as a function of the total number of holes through a linear interpolation of the Green functions. The stoichiometric compound is a charge transfer insulator in the antiferromagnetic phase. Magnetic order is destroyed at different concentrations for electron and hole doping. ((orig.))