Mobile Zhang-Rice singlets: Electron correlations and bond-length fluctuations in copper oxides

We perform first principles, multiconfiguration calculations on clusters including several CuO6 octahedra and study the ground-state electron distribution and electron-lattice couplings when holes are added to the undoped d(9)p(6) configuration. We find that the so-called Zhang-Rice state on a single CuO4 plaquette is nearly degenerate with a state whose leading configuration is of the form Cu d(9)-O p(5)-Cu d(9). A strong coupling between the electronic and nuclear motions gives rise to large inter-site charge transfer effects for half-breathing displacements of the oxygen ions. Under the assumption of charge segregation into alternating hole-free and hole-rich stripes, our results seem to support the vibronic mechanism and the traveling charge-density wave model proposed by J. B. Goodenough [J. Phys.: Condens. Matter 15, R257 (2003)] for the superconductivity in copper oxides.