1 research outputs found
Heisenberg exchange enhancement by orbital relaxation in cuprate compounds
We calculate the Heisenberg exchange J in the quasi-2D antiferromagnetic
cuprates La2CuO4, YBa2Cu3O6, Nd2CuO4 and Sr2CuO2Cl2. We apply all-electron
(MC)SCF and non-orthogonal CI calculations to [Cu2O11]18-, [Cu2O9]14-,
[Cu2O7]10- and [Cu2O7Cl4]14- clusters in a model charge embedding. The (MC)SCF
triplet and singlet ground states are well characterized by Cu2+ (dx2-y2) and
O2-. The antiferromagnetic exchange is strongly enhanced by admixing relaxed
(MC)SCF triplet and singlet excited states, in which a single electron is
transferred from the central O ion to Cu. We ascribe this effect to orbital
relaxation in the charge transfer component of the wave function. Close
agreement with experiment is obtained.Comment: publishe