[gmx-users] About the "I" ion, Na ion issue for Gromacs force field

[Yuhua Song]

Dear Gromacs-mailing list:

I intend to simulate a system with "I" ion effect using the Gromacs force field. 
When I check the ions.itp, newions.itp, ffgmxnb.itp etc, I can not find "I" ion for Gromacs force field,

Could I just define the "I" as below, and used for my simulation:

[ moleculetype ]
; molname       nrexcl
I               1
[ atoms ]
; id    at type res nr  residu name     at name  cg nr  charge   mass
1       I       1       I               I        1      -1       126.9045
                                                                               
#ifdef POSRES_I
#include "I_posre.itp"
#endif


Also, in the newions.itp and ions.itp, the definition for NA for Gromacs force field is:
[ moleculetype ]
; molname       nrexcl
Na              1
                                                                               
[ atoms ]
; id    at type res nr  residu name     at name  cg nr  charge
1       Na      1       Na              Na       1      1
                                                                               

If I define the NA is the following way, and used in my simulation using Gromacs force field , it will cause problem?

[ moleculetype ]
; molname       nrexcl
NA              1
                                                                               
[ atoms ]
; id    at type res nr  residu name     at name  cg nr  charge
1       NA      1       NA              NA       1      1
                                                                               
#ifdef POSRES_NA
#include "NA_posre.itp"
#endif


Thank you very much.