Adding ion to a force field

[esmee]

GROMACS version: 2021.3
GROMACS modification: Yes

Dear GROMACS users,

I would like to add an ion to a force field. The residue for the neutral atom corresponding to the ion is already present in the force field. Which files have to be modified and how?

[alevilla]

Hi,
See my answer to your previous post. I hope it cover all the points

Properly including bromide in GROMOS96 54a7

Hi, The reason is that you change the name from BR → BR- and BR- is not defined as atomtype in the force field files. Atom type information are storage in ffnonbonded.itp in the [ atomtypes ] directive and [ nonbond_params ] directive (for gromos force field) and in the database atomtypes.atp. To know more on the format see File formats — GROMACS 2022.3 documentation yes. BR and BR- are different, it is more appropriate to describe them using different LJ parameters. When you add a…

\Alessandra