[gmx-users] Force field parameter for Fe, Mo, Mn, Cd, Ni and Co.

[majid foroughi]

Hello,
I am using Gromacs version 4.6.6 and GROMOS96 53a6 force field.I am studying a metalloprotein with zinc in active site, now I wanna substitute the zinc ion with other metal ions such as Fe, Mo, Mn, Cd, Ni and Co, to see the protein stability and other features. But cannot make topology file for the protein with these metal ions because the force field is not parametrised for these ions. 
Now my question is, where can I find the data required to parametrized these metal ions in the gromacs force field. Also I wish to be guided on the approach how to parametrize these metal ions. Thank you
Majid Foroughi