DENSITY-FUNCTIONAL CALCULATIONS OF MAGNETIC EXCHANGE INTERACTIONS IN POLYNUCLEAR TRANSITION-METAL COMPLEXES

Two effective computational approaches for the study of magnetic excha nge interactions in large molecules are discussed and tested on a numb er of model systems, namely, broken-symmetry (BS) and single-determina nt (SD) models. Both methods are based on the density functional theor y (DFT) but exploit different approximations to deal with multiconfigu rational problems. Our results show that the BS model provides semiqua ntitative results for widely different situations, such as metal-radic al interactions and metal-metal interactions mediated by inert organic bridges. Although more refined (and expensive) methods are needed for truely quantitative work, the BS/DFT approach provides a very useful tool for the rationalization of magneto-structural correlations and fo r the comparison of different bonding situations in large systems invo lving transition metal atoms.