Towards an<i>ab initio</i>description of magnetism in ionic solids

Abstract

The physical contributions to the ${\mathrm{KNiF}}_{3}$ magnetic exchange coupling integral have been obtained from specially designed ab initio cluster model calculations. Three important mechanisms have been identified. These are the delocalization of the magnetic orbitals into the anion ``p'' band, the variational contribution of the second-order interactions, and the many-body terms ``hidden'' in the two-body operator and the Heisenberg Hamiltonian.