Heisenberg exchange in La2CuO4

Abstract

We study the exchange interaction in the quasi-2D antiferromagnetic high Tc superconductor parent compound La2CuO4 by all-electron, embedded cluster methods. Our material model is the cluster Cu2O11, embedded in a matrix of point charges. The SCF ground state configuration is characterized by Cu 2+ and O2− with the d-hole oriented in the [CuO2]2− plane along the CuO bonds. We admix to this an excited SCF configuration that has one Cu-hole transferred to the central O into the ground state configuration by nonorthogonal CI, while paying special attention to the variational balance of the singlet and triplet states. This results in a value for the exchange parameter of J = −120 meV, in good agreement with the experimental value of J = −128 meV. © 1995 John Wiley & Sons, Inc.