DENSITY-FUNCTIONAL MODELING OF DOUBLE EXCHANGE INTERACTIONS IN TRANSITION-METAL COMPLEXES - CALCULATION OF THE GROUND AND EXCITED-STATE PROPERTIES OF [FE-2(OH)(3)(TMTACN)(2)](2+)

Density functional theory has been successfully applied to characteriz e the electronic structure and the magnetic properties of the mixed va lence dinuclear complex [Fe-2(OH)(3)(tmtacn)(2)](2+) modeled by replac ing the tmtacn ligand with three ammonia molecules. Spectroscopic and magnetic properties have been computed in nice agreement with the expe rimental values. Minimum energy path calculations allowed us to comput e the frequencies associated with the normal coordinate Q(-) responsib le for the delocalization of the extra electron, and we resent here a procedure for the full characterization of mixed-valence transition me tal dimers.