Electronic structure and correlations of high-temperature superconducting compounds.

Abstract

Calculations on negatively charged planar ${\mathrm{Cu}}_{\mathit{n}}$${\mathrm{O}}_{\mathit{m}}$ clusters are reported. Starting from a self-consistent-field calculation within a good Gaussian-type-orbital basis set, correlations are included using the local ansatz. A charge analysis reveals a Cu 3d occupation in close agreement with calculations in the local-density approximation. The electrons in the formal ${\mathrm{Cu}}_{\mathit{n}}^{2+}$${\mathrm{O}}_{\mathit{m}}^{2\mathrm{\ensuremath{-}}}$ entities are delocalized between Cu and O sites and strongly correlated. Our findings do not agree with the assumption of localized ${\mathrm{Cu}}^{2+}$ spins which is often made in models for these compounds. Spin correlations indicate strong short-range antiferromagnetic order even if electrons are removed. For them, there is no difference between O and Cu sites.