Model molecular magnets

The local spin method suggested previously for defining the spin state of an atom in a molecule is applied to model manganese complexes with three and four manganese centers. This method extracts from the wave function a spin for the manganese centers that has been compared to the one suggested by chemical intuition. Density functional theory (DFT) calculations with various total spin projections in the "up" direction, M, but controlled \M\ for each manganese center, gave a set of energies that were fit to the Heisenberg Hamiltonian. The eigenvalues of this model Hamiltonian then predict the ground spin state and the preferred combinations of spin orientations of the manganese centers. In some model complexes, changes in the wave function for each spin solution made the Heisenberg Hamiltonian unsuitable for fitting. For a dinuclear manganese complex, complete active space self-consistent field calculations were performed and are in reasonable agreement with the DFT results.