THE ROLE OF APICAL OXYGEN IN THE HIGH-TEMPERATURE SUPERCONDUCTORS

We report finite-cluster diagonalizations which clarify the role of ap ical oxygen orbitals and of the copper d(3z2-r2) orbitals in the groun d-state electronic properties of high-temperature superconductors. The hole density distribution and spin-spin correlation functions are ana lysed as functions of interoxygen hopping and other parameters. The ma in conclusion is that for universally accepted parameters for CuO2 pla nes, small levels of doping and no phonons, the three-band Hamiltonian suffices to describe the properties of the ground state and the inver se photoemission.