[gmx-users] where do Zinc parameters come from ?

[CROUZY Serge 119222]

Hello users

Can anyone tell me where the LJ parameters for Zn2+ come from in the Gromacs gromos54a7.ff force field ?
(Literature reference for instance) 

;name  at.num   mass      charge  ptype       c6           c12
 ZN2+   30      0.000      0.000     A  0.0004182025  9.4400656e-09

I'm actually looking for parameters for Fe2+ which I could try to derive using the same approach 
(I know these nonbonded parameters will remain a poor approximation of the mertal behavior but I'm only interested in keeping the metal site "geometrically sound")

Thanks