Electronic structure of square planar CuO₄⁶⁻ clusters

Abstract

The results of spin-polarized MSXα calculations show that the ground state of the CuO₄⁶⁻ cluster is essentially non-magnetic in spite of odd number of electrons in the system for short Cu-O distances (1.90 Å) as found in the high T_c superconductors. This arises due to the fact that the unpaired electron resides in a molecular orbital with primarily oxygen 3s character. The stability of this molecular orbital is found to be sensitive to the cluster geometry and thus, increase in Cu-O distance (as well as other changes affecting oxygen-oxygen distance) tend to favour a magnetic state. From these calculations we have also estimated the Coulomb correlation strength within the Cu 3d to be about 5.3 eV.