I have been trying to calculate Zn partial charge in glyoxalase 1 enzyme. Zn is coordinating with 4 amino acid residues and 2 water molecules forming a perfect octahedral. Those 2 water molecules are usually replaced by a ligand thus mainatning the coordinating geoimetry. 

To calculate accurate Zn+2 charge, I used DS DFT single point calculation. I shortened the coordinating amino acids (CH3OOH for aspartate, Imidazole for His ,and so on), ran the DFT protocol (Dmol3) and calculated ESP partial charges. Zn+2 charge was +1.255 (instead of +2 in CHARMm), Can I use this charge (ESP) directly in the CHARMm forcefield? 
what additional parameters can I obtain from QM to incorporate in the forcefield ?

(Dmol3,Level:BLY3P,, Implicit solvent: chloroform (dielectric constant = 4, pretty much like a protein), Quality: Fine)