A DFT based ligand field model for magnetic exchange coupling in homonuclear transition metal dimmer complexes is presented. It is based on a model of localized d-electrons and on a procedure allowing to express its parameters in terms of exchange and Coulomb integrals from DFT calculations of a homonuclear dimmer complex. We describe a recipe to relate the latter integrals with the manifold of all Slater determinants of the active space originating from the magnetic electrons of the dimmer. The method is applied to d(9) and d(1) model clusters involving Cu-11 and Ti2Cl93- and has been extended to cases with more than one impaired electron per site. (C) 2003 Elsevier B.V. All rights reserved.