# Query regarding gmx error for sld.prm file while generating ions.tpr file
**URL:** https://gromacs.bioexcel.eu/t/query-regarding-gmx-error-for-sld-prm-file-while-generating-ions-tpr-file/698
**Category:** User discussions
**Created:** [August 24, 2020, 1:21pm UTC](https://gromacs.bioexcel.eu/t/query-regarding-gmx-error-for-sld-prm-file-while-generating-ions-tpr-file/698 "2020-08-24T13:21:19Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@deetijyothi1](https://gromacs.bioexcel.eu/u/deetijyothi1)
#### Post date: [August 24, 2020, 1:21pm UTC](https://gromacs.bioexcel.eu/t/query-regarding-gmx-error-for-sld-prm-file-while-generating-ions-tpr-file/698/1 "2020-08-24T13:21:19Z")
GROMACS version:2020.3
GROMACS modification: Yes/No
when I am running the command:
$ gmx\_mpi grompp -f ions.mdp -c solv.gro -p topol.top -o ions.tpr
I am getting error like:
ERROR 1 [file sld.prm, line 4]:
Unknown bond\_atomtype CG2C1
How to sort out this
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### Author:  [@jalemkul](https://gromacs.bioexcel.eu/u/jalemkul)
#### Post date: [August 24, 2020, 5:43pm UTC](https://gromacs.bioexcel.eu/t/query-regarding-gmx-error-for-sld-prm-file-while-generating-ions-tpr-file/698/2 "2020-08-24T17:43:20Z")
Where did this `.prm` file come from? Did you modify it in any way? CG2C1 is not a valid atom type in CGenFF.
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### Author:  [@deetijyothi1](https://gromacs.bioexcel.eu/u/deetijyothi1)
#### Post date: [August 25, 2020, 4:22am UTC](https://gromacs.bioexcel.eu/t/query-regarding-gmx-error-for-sld-prm-file-while-generating-ions-tpr-file/698/3 "2020-08-25T04:22:09Z")
.prm file will generate when we run the command ‘python cgenff\_charmm2gmx.py JZ4 jz4\_fix.mol2 jz4.str charmm36-mar2019.ff’. Can anyone please suggest to me, do we need to add hydrogens for docking complex separated protein-ligand files before starting MDS? Thanks in advance.
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### Author:  [@jalemkul](https://gromacs.bioexcel.eu/u/jalemkul)
#### Post date: [August 25, 2020, 3:01pm UTC](https://gromacs.bioexcel.eu/t/query-regarding-gmx-error-for-sld-prm-file-while-generating-ions-tpr-file/698/4 "2020-08-25T15:01:05Z")
For CHARMM, which is an all-atom force field, yes.
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### Author:  [@deetijyothi1](https://gromacs.bioexcel.eu/u/deetijyothi1)
#### Post date: [September 9, 2020, 2:21pm UTC](https://gromacs.bioexcel.eu/t/query-regarding-gmx-error-for-sld-prm-file-while-generating-ions-tpr-file/698/5 "2020-09-09T14:21:30Z")
Greetings!!!
Yes. I used CHARMM36 all-atom force field (July 2017)