# Script conversion problem

**URL:** <https://gromacs.bioexcel.eu/t/script-conversion-problem/2204>\
**Category:** User discussions\
**Created:** [May 22, 2021, 10:02am UTC](https://gromacs.bioexcel.eu/t/script-conversion-problem/2204 "2021-05-22T10:02:32Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![gromacsnoob234](https://avatars.discourse-cdn.com/v4/letter/g/94ad74/32.png) [@gromacsnoob234](https://gromacs.bioexcel.eu/u/gromacsnoob234)\
**Post date:** [May 22, 2021, 10:02am UTC](https://gromacs.bioexcel.eu/t/script-conversion-problem/2204/1 "2021-05-22T10:02:32Z")

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GROMACS version: 2019  
GROMACS modification: No  
Here post your question

I am trying to paramaterize an analog of glucose. When I use script cgenff\_charmm2gmx.py downloaded from the MacKerell website to convert ParamChem CGenFF toppar stream file from CHARMM to GROMACS format.

python cgenff\_charmm2gmx\_py3\_nx1.py BGC\_fix.mol2 BGC.str charmm36-feb2021.ff  
What I get is this: Usage: RESNAME drug.mol2 drug.str charmm36.ff  
How to fix this in order to generate my itp file?

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**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 23, 2021, 1:30am UTC](https://gromacs.bioexcel.eu/t/script-conversion-problem/2204/2 "2021-05-23T01:30:34Z")

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You didn’t specify a residue name, which is the first required argument as noted in the error message.

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<div class="post-metadata">

**Author:** ![AndreaMx](https://avatars.discourse-cdn.com/v4/letter/a/ee7513/32.png) [@AndreaMx](https://gromacs.bioexcel.eu/u/AndreaMx)\
**Post date:** [March 13, 2025, 1:33am UTC](https://gromacs.bioexcel.eu/t/script-conversion-problem/2204/3 "2025-03-13T01:33:55Z")

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Hi I have the same error, but I don´t know how to specify a residue name  
Could you give a deeper explanation?

 ![Captura de pantalla 2025-03-12 a la(s) 7.33.27 p.m.](https://europe1.discourse-cdn.com/flex017/uploads/bioexcel1/original/2X/a/a7f39ed74c64a8d1924b0b384658ca3ae59b1091.png)  
please!

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<div class="post-metadata">

**Author:** ![Ashutosh](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/ashutosh/32/2587_2.png) [@Ashutosh](https://gromacs.bioexcel.eu/u/Ashutosh)\
**Post date:** [March 13, 2025, 3:20am UTC](https://gromacs.bioexcel.eu/t/script-conversion-problem/2204/4 "2025-03-13T03:20:23Z")

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bro see you are using .mol2 and .str file. now you have to do is that open them and find all RESNAME and make them into 3 letter word like lig or something else but 3 letter only. that will not give any error. you just have open file in notepad and then ctrl + F and type RESNAME and in replace option type any 3 letter word and replace all at once and save them.

```auto
python3 cgenff_charmm2gmx.py lig lig_fix.mol2 lig_fix.str charmm36-jul2022.ff

```