The protein I am using in the structure-based pharmacophore has a metal (Mg), which is very important in the protein-ligand interation.I prepared the protein using protein preparation protocol, and then generated the pharmacophore as the standard procedure. But Discovery_studio2.5 seems not recognizing the metal, because there is no pharmacophore being generated from the metal. How can I generate a pharmacophore from a metal and which type of pharmacophore it should be?