Electron correlations and bond-length fluctuations in copper oxides: from Zhang--Rice singlets to correlation bags

Abstract

We perform first principles, multiconfiguration calculations on clusters including several CuO${}_6$ 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 CuO${}_4$ 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 motion 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 of Goodenough \cite{jbg_02,jbg_03}, our results seem to support the vibronic mechanism and the traveling charge-density wave model from Refs.\cite{jbg_02,jbg_03} for the superconductivity in copper oxides.

submitted to Phys. Rev. B

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