HEISENBERG EXCHANGE IN LA2CUO4

We study the exchange interaction in the quasi-2D antiferromagnetic high T-c 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 CU2+ 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 a, 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. (C) 1995 John Wiley & Sons, Inc.