# Error in adding ions using CHARMM36m **URL:** \ **Category:** User discussions\ **Created:** [June 10, 2022, 10:31pm UTC](https://gromacs.bioexcel.eu/t/error-in-adding-ions-using-charmm36m/4287 "2022-06-10T22:31:49Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![asaf.farhi](https://avatars.discourse-cdn.com/v4/letter/a/b9bd4f/32.png) [@asaf.farhi](https://gromacs.bioexcel.eu/u/asaf.farhi)\ **Post date:** [June 10, 2022, 10:31pm UTC](https://gromacs.bioexcel.eu/t/error-in-adding-ions-using-charmm36m/4287/1 "2022-06-10T22:31:49Z")
GROMACS version: GROMACS modification: Yes/No Here post your question Hi all, I’m using gromcs with CHARMM36m ff. When I use an earlier CHARMM ff it works well. When adding ions using mpirun -np 1 gmx\_mpi grompp -f ions.mdp -c pdb\_solv.gro -p topol.top -o ions.tpr it writes ERROR 1 [file topol\_Protein\_chain\_B.itp, line 1818]: No default Proper Dih. types This line is: 1 4 17 19 9 NH2-CT1-C-N Might be related to terminal residue NH2. Thank you for your time and consideration, Best regards, Asaf ---
**Author:** ![jalemkul](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/jalemkul/32/18_2.png) [@jalemkul](https://gromacs.bioexcel.eu/u/jalemkul)\ **Post date:** [June 11, 2022, 2:36am UTC](https://gromacs.bioexcel.eu/t/error-in-adding-ions-using-charmm36m/4287/2 "2022-06-11T02:36:22Z")
> [@asaf.farhi](#): > > I’m using gromcs with CHARMM36m ff. When I use an earlier CHARMM ff it works well. Can you please specify which release you are using that has a problem, and which was correct? This parameter should have been added to the force field several years ago when users encountered the same problem. ---
**Author:** ![asaf.farhi](https://avatars.discourse-cdn.com/v4/letter/a/b9bd4f/32.png) [@asaf.farhi](https://gromacs.bioexcel.eu/u/asaf.farhi)\ **Post date:** [June 12, 2022, 2:38pm UTC](https://gromacs.bioexcel.eu/t/error-in-adding-ions-using-charmm36m/4287/3 "2022-06-12T14:38:14Z")
Thanks a lot for your response. I really appreciate it. Sure, I’m using gromacs/2020.2-cpu with charmm36-jul2021. The previous one that works well with the same gromacs version is CHARMM27 all-atom force field (CHARM22 plus CMAP for proteins). This may be related to capping a terminal residue with NH2 in pdb2gmx etc. Thank you for your time and consideration, Best regards, Asaf ---
**Author:** ![jalemkul](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/jalemkul/32/18_2.png) [@jalemkul](https://gromacs.bioexcel.eu/u/jalemkul)\ **Post date:** [June 14, 2022, 6:55pm UTC](https://gromacs.bioexcel.eu/t/error-in-adding-ions-using-charmm36m/4287/4 "2022-06-14T18:55:28Z")
I will look and see what is going on with CHARMM36; my statement before was that, to my knowledge, we had fixed this issue in the CHARMM36 port by introducing a parameter by analogy, which was included upstream in the parent CHARMM distribution. It therefore should have been included automatically in our latest port. I was hoping to track down where that might have been lost in the CHARMM36 lineage (which is distinct from the CHARMM27 files produced by the GROMACS team in 2010). ---
**Author:** ![asaf.farhi](https://avatars.discourse-cdn.com/v4/letter/a/b9bd4f/32.png) [@asaf.farhi](https://gromacs.bioexcel.eu/u/asaf.farhi)\ **Post date:** [June 14, 2022, 7:16pm UTC](https://gromacs.bioexcel.eu/t/error-in-adding-ions-using-charmm36m/4287/5 "2022-06-14T19:16:07Z")
Great, thanks a lot. I really apprecaite it. As a followup question there is the option to choose CT2 for the C terminal in gromacs -ter flag and we were wondering if: 1. It means that it caps the residue to CT2? 2. If so, is there an option to cap the N terminal with ACE? Thank you again for your time and consideration, Best regards, Asaf ---
**Author:** ![jalemkul](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/jalemkul/32/18_2.png) [@jalemkul](https://gromacs.bioexcel.eu/u/jalemkul)\ **Post date:** [June 15, 2022, 1:08pm UTC](https://gromacs.bioexcel.eu/t/error-in-adding-ions-using-charmm36m/4287/6 "2022-06-15T13:08:35Z")
> [@asaf.farhi](#): > > - It means that it caps the residue to CT2? Yes. > [@asaf.farhi](#): > > If so, is there an option to cap the N terminal with ACE? Not via `.tdb` because there is limited ability to construct atoms. You need to have an actual ACE residue defined as the N-terminal species, and choose “None” as the terminus type when prompted. ---
**Author:** ![asaf.farhi](https://avatars.discourse-cdn.com/v4/letter/a/b9bd4f/32.png) [@asaf.farhi](https://gromacs.bioexcel.eu/u/asaf.farhi)\ **Post date:** [June 17, 2022, 5:25pm UTC](https://gromacs.bioexcel.eu/t/error-in-adding-ions-using-charmm36m/4287/7 "2022-06-17T17:25:11Z")
Thanks a lot for your help. Best regards, Asaf