# Adding ion to a force field

**URL:** <https://gromacs.bioexcel.eu/t/adding-ion-to-a-force-field/4918>\
**Category:** User discussions\
**Created:** [September 29, 2022, 12:31pm UTC](https://gromacs.bioexcel.eu/t/adding-ion-to-a-force-field/4918 "2022-09-29T12:31:34Z")\
**Posts on this page:** 1\
**Showing post:** 2

<div class="post-metadata">

**Author:** ![alevilla](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/alevilla/32/439_2.png) [@alevilla](https://gromacs.bioexcel.eu/u/alevilla)\
**Post date:** [September 30, 2022, 11:41am UTC](https://gromacs.bioexcel.eu/t/adding-ion-to-a-force-field/4918/2 "2022-09-30T11:41:05Z")

</div>

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

> [@Properly including bromide in GROMOS96 54a7](https://gromacs.bioexcel.eu/t/properly-including-bromide-in-gromos96-54a7/4836/3):
>
> 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](https://manual.gromacs.org/current/reference-manual/topologies/topology-file-formats.html) yes. BR and BR- are different, it is more appropriate to describe them using different LJ parameters. When you add a…

\Alessandra

---

_[View the full topic](https://gromacs.bioexcel.eu/t/adding-ion-to-a-force-field/4918)._