# How to solve 'Unknown bond\_atomtype error'?

**URL:** <https://gromacs.bioexcel.eu/t/how-to-solve-unknown-bond-atomtype-error/170>\
**Category:** User discussions\
**Created:** [May 22, 2020, 1:16pm UTC](https://gromacs.bioexcel.eu/t/how-to-solve-unknown-bond-atomtype-error/170 "2020-05-22T13:16:03Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![Jinyoung](https://avatars.discourse-cdn.com/v4/letter/j/3be4f8/32.png) [@Jinyoung](https://gromacs.bioexcel.eu/u/Jinyoung)\
**Post date:** [May 22, 2020, 1:16pm UTC](https://gromacs.bioexcel.eu/t/how-to-solve-unknown-bond-atomtype-error/170/1 "2020-05-22T13:16:03Z")

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GROMACS version: 2019.4  
GROMACS modification: Yes

Dear GROMACS users,  
I’ve simulated the protein-ligand complex system with charmm36-jul2017 force field.  
I generated the ligand topology/parameter files from the cgenff and cgenff\_charmm2gmx\_py3\_nx.py file. and there is no problem until I used the ‘gmx grompp’. Even the ‘gmx pdb2gmx’ didn’t raise error.

But when I issued the command line below:

```
gmx_mpi grompp -f MDP/ions.mdp -c COMPLEX/complex_solv.gro -p TOP/topol.top -o COMPLEX/ions.tpr 

```

Fatal error came up

ERROR 1 [file lig.prm, line 12]:  
Unknown bond\_atomtype CG2R61

I attached my lig.prm file generated by cgenff\_charmm2gmx\_py3\_nx.py

```
[bondtypes]
; i j func b0 kb

[angletypes]
; i j k func theta0 ktheta ub0 kub

[dihedraltypes]
; i j k l func phi0 kphi mult
CG2R61 CG321 CG321 NG311 9 0.000000 0.167360 3
CG321 CG321 NG311 SG3O2 9 0.000000 0.418400 1
CG321 CG321 NG311 SG3O2 9 0.000000 2.928800 2
CG321 CG321 NG311 SG3O2 9 0.000000 0.418400 3
CG321 CG321 NG311 HGP1 9 0.000000 0.418400 3

[dihedraltypes]
; 'improper' dihedrals
; i j k l func phi0 kphi

```

Any ideas? Thank you for reply in advance

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<div class="post-metadata">

**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:** [May 22, 2020, 1:31pm UTC](https://gromacs.bioexcel.eu/t/how-to-solve-unknown-bond-atomtype-error/170/2 "2020-05-22T13:31:56Z")

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CG2R61 is a standard CGenFF atom type and is defined in `ffnonbonded.itp`. There should be no problem using this atom type unless you have edited the parent force field in some way or have otherwise not `#included` it in your topology.

Note that there is a newer (March 2019) version of the CHARMM36 port that includes parameter updates. That is not relevant to this particular issue (CG2R61 is in both versions), but FYI.

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<div class="post-metadata">

**Author:** ![Jinyoung](https://avatars.discourse-cdn.com/v4/letter/j/3be4f8/32.png) [@Jinyoung](https://gromacs.bioexcel.eu/u/Jinyoung)\
**Post date:** [May 22, 2020, 1:43pm UTC](https://gromacs.bioexcel.eu/t/how-to-solve-unknown-bond-atomtype-error/170/3 "2020-05-22T13:43:57Z")

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you’re right. The wrong force field name was wrote in my topology file. It’s all my fault. Thank you for your reply :)  
And I did actually run MD simulation with CHARMM36 2019 force field, but when I used the g\_mmpbsa tool with CHARMM36 2019, ‘Cannot allocate memory’ error rised. So I reduced the trajectory file size by using ‘gmx trjconv’ and it did not solve the ‘Cannot allocate memory’ error.  
Therefore because I assumed the reason is that CHARMM36 2019 force filed is not compatitable with g\_mmpbsa, I’m trying to run with CHARMM36 2017 force field

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<div class="post-metadata">

**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:** [May 22, 2020, 1:55pm UTC](https://gromacs.bioexcel.eu/t/how-to-solve-unknown-bond-atomtype-error/170/4 "2020-05-22T13:55:31Z")

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I doubt that will solve the problem. The force field versions are mostly the same, and there is no reason to think that there is some specific issue with the CHARMM force field and `g_mmpbsa`. That is not an officially supported program, so there is no way to know if it is properly updated and maintained.

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<div class="post-metadata">

**Author:** ![Jinyoung](https://avatars.discourse-cdn.com/v4/letter/j/3be4f8/32.png) [@Jinyoung](https://gromacs.bioexcel.eu/u/Jinyoung)\
**Post date:** [May 26, 2020, 12:18am UTC](https://gromacs.bioexcel.eu/t/how-to-solve-unknown-bond-atomtype-error/170/5 "2020-05-26T00:18:27Z")

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Thank you for your quickly reply.  
It is right. So I have tried to reinstall with another version of g\_mmpbsa.

Thank you again