If the metal site is not of central interest in the investigation, for example, a structural metal far from the active site, a simple and fast parametrization is normally enough, using either a nonbonded model with restraints or a bonded parametrization based on the method of Seminario， e.g. Antechamber，Hess2FF, 

if the metal site is of central interest in the investigation, a more accurate method is needed to give quantitative results, for example, the method by Norrby and Liljefors. 

water ligands pose severe problems for bonded models in force fields that ignore nonbondedinteractions for atoms separated by two bonds. Complexes with a single water ligand can normally be accurately treated with a bonded potential, once it is ensured that the water H atoms have nonzero Lennard-Jones parameters. However, for metal sites with several water molecules, a nonbonded model with restraints (taken from the QM calculations) is more stable.