Non-orthogonal orbitals for localized electrons - II. Variational optimization based on an effective spin hamiltonian

The derivation of an effective spin hamiltonian is achieved for a single co nfiguration Spin-Coupled Valence Bond wavefunction built upon weakly overla pping non-orthogonal orbitals. The effective Spin-Coupled Magnetic Hamilton ian (SCMH) serves for the variational optimization of both orbital and spin parts of the wavefunction for larger numbers of electrons than genuine qua ntum-chemical methods. Optimized magnetic coupling terms are thus obtained. The method is applied to localized electrons within the one-dimensional ha lf-filled Hubbard model yielding magnetic coupling constants that are in go od agreement with reference Spin-Coupled calculations on finite size cluste rs and perturbation theory in the localized regime. (C) 1999 Elsevier Scien ce B.V. All rights reserved.