J.E. Hirsch and S. Tang, Phys.Rev. B40, 2179 (1989)
We study the properties of an effective Hamiltonian to describe the propagation of holes through the oxygen anion network in a high-Tc superconductor. Approximate parameters for our Hamiltonian are derived from atomic properties of O. The effective interaction between holes and the effective bandwidth for the holes are studied by diagonalization of finite clusters. The effective interaction is found to be attractive for realistic parameters; in the same regime, there is significant band narrowing. Consequences of our results for normal and superconducting properties of high Tc oxides are discussed.