[gmx-users] surrounding a peptide by ions of magnesium

[Mohan maruthi sena]

Hi all,
           I have system consisting of a peptide(alpha-helix), I want the
peptide to be surrounded by magnesium ions(instead of water). How can i do
this gromacs? How can I find the concentration of magnesium ions. just like
in solution we have 0.5 Molar  Mg+2  solution, My question how can  find
concentration by increasing number of ions.

Thanks for a reply in advance,

Mohan