CONSISTENT LOW-ENERGY REDUCTION OF THE 3-BAND MODEL FOR COPPER OXIDESWITH O-O HOPPING TO THE EFFECTIVE T-J MODEL

A full three-band model for the CuO2 plane with inclusion of all essen tial interactions-Cu-O and O-O hopping, repulsion at the copper and ox ygen and between them-is considered. A general procedure of the low-en ergy reduction of the primary Hamiltonian to the Hamiltonian of the ge neralized t-t'-J model is developed. An important role of the direct O -O hopping is discussed. Parameters of the effective low-energy model (the hopping integral, the band position, and the superexchange consta nt J) are calculated. An analysis of the obtained data shows that the experimental value of J fixes the charge-transfer energy DELTA = (epsi lon(p) - epsilon(d)) in a narrow region of energies.