# ERROR No such moleculetype

**URL:** <https://gromacs.bioexcel.eu/t/error-no-such-moleculetype/6555>\
**Category:** User discussions\
**Tags:** forcefield, simulation-setup\
**Created:** [June 6, 2023, 4:09pm UTC](https://gromacs.bioexcel.eu/t/error-no-such-moleculetype/6555 "2023-06-06T16:09:23Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![jane\_hi](https://avatars.discourse-cdn.com/v4/letter/j/a698b9/32.png) [@jane\_hi](https://gromacs.bioexcel.eu/u/jane_hi)\
**Post date:** [June 6, 2023, 4:09pm UTC](https://gromacs.bioexcel.eu/t/error-no-such-moleculetype/6555/1 "2023-06-06T16:09:23Z")

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GROMACS version: 2020  
GROMACS modification: No  
forcefield I am using: charmm36  
Here post your question:

Hi,  
I ran grompp -f EM.mdp -c system.pdb -p system.top -o em.tpr and I got this error:

_ERROR 1 [file system\_GMX\_charmm36.top, line 22]:_

- No such moleculetype sls \*

_-------------------------------------------------------_  
_Program: gmx grompp, version 2020_  
_Source file: src/gromacs/gmxpreprocess/toppush.cpp (line 2511)_

_Fatal error:_  
_There was 1 error in input file(s)_

By the way, I have the same error for other molecule types as well when I remove molecule sls. Attached is my topology file. I have included sls molecule type in sls.itp. And I tried dos2unix to convert the topology file but didn’t fix the issue.

[system\_GMX\_charmm36.top](https://gromacs.bioexcel.eu/uploads/short-url/gXy63WPLZtY8XYFTTA9Qc8MnAXQ.top) (891 Bytes)