[Chimera-users] Electrostatic Potential

Hi I am just calculating the Electrostatic Potential, and I wanted to know your opinion which force field is better for metallo proteins.And what is criteria to choose and not to choose the pKA... As I am doing the reaction at different pH and what I see in the PDB the proteins are crystallized at different pH then the reaction conditions. Structures are solved at low pH but the reactions are done at high pH. best Jiri