Lattice and polarizability effects on singlet and triplet states in an effective hamiltonian for high-T-c cuprates

From various theoretical approaches it seems to be rather well established that the Zhang-Rice (ZR) singlet state should play an important role in dop ed high-temperature superconducting (HTSC) oxides. Yet the conclusion that a one-band model is capable of describing many of the unusual physics obser ved in HTSC compounds has been questioned because the p(z) states of the ox ygen atoms in the planes;as well as those of the apical oxygen atoms hybrid ize with the Cu d(3z2-r2) orbitals and induce a mixing of the in-plane stat es with the out-of-plane bands. It is shown that electron-lattice coupling and polarizability effects modify the electronic structure of the effective Hamiltonian considered here.