A canonical transformation method is used to derive an effective Hamiltonian which describes Cu(3d) spins and O(2p) holes within the CuO2 plane in the charge transfer regime. It is found that spin-carrier interactions present in second order overrule the pairing mechanisms as proposed by Emery (1987) and Hirsch. (1987). The results suggest that the mixed valence regime is more realistic for high Tc superconductors.
 

Physica C, 153-155 1229-30, 1988.