structures and spectromagnetic properties of some model copper nitroxide complexes were studied by both density functional and multireference post-Hartree-Fock models in order to assess the reliability of different computational procedures. Next, the most promising density functional was employed for a systematic study of the effect of structural parameters and choice of the model system on the magnetic properties of copper nitroxides. These results provided the reference data for the extension of our recent nitroxide force field (J. Am. Chem. Sec. 1998, 120, 7069) to copper complexes. The resulting computational tool (consisting of magnetic properties evaluated by density functional methods possibly using geometries optimized by cheaper moleculear mechanics approaches) seems particularly effective and well suited for systematic use also by nonspecialists. Extension to other metals is quite straightforward along the same lines.