# Problem for generating charmm topol file by CGenFF

**URL:** <https://gromacs.bioexcel.eu/t/problem-for-generating-charmm-topol-file-by-cgenff/1226>\
**Category:** User discussions\
**Created:** [December 8, 2020, 3:06pm UTC](https://gromacs.bioexcel.eu/t/problem-for-generating-charmm-topol-file-by-cgenff/1226 "2020-12-08T15:06:19Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![JieChen](https://avatars.discourse-cdn.com/v4/letter/j/ea5d25/32.png) [@JieChen](https://gromacs.bioexcel.eu/u/JieChen)\
**Post date:** [December 8, 2020, 3:06pm UTC](https://gromacs.bioexcel.eu/t/problem-for-generating-charmm-topol-file-by-cgenff/1226/1 "2020-12-08T15:06:19Z")

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GROMACS version: 2019.4-plumed  
GROMACS modification: Yes  
Here post your question

I generated str file on the web of CGenFF. When I run it through the command " python cgenff\_charmm2gmx.py Sketch jiasuan.mol2 jiasuan.str charmm27.ff " meeting the following problem. How should I do?

 ![屏幕截图 2020-12-08 230432](https://europe1.discourse-cdn.com/flex017/uploads/bioexcel1/original/1X/69ebfe3878236e663ef5f74c913cb5fe1be731de.jpeg)

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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:** [December 8, 2020, 3:17pm UTC](https://gromacs.bioexcel.eu/t/problem-for-generating-charmm-topol-file-by-cgenff/1226/2 "2020-12-08T15:17:31Z")

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You can’t use CHARMM27 with CGenFF. Download the CHARMM36 port from [http://mackerell.umaryland.edu/charmm\_ff.shtml#gromacs](http://mackerell.umaryland.edu/charmm_ff.shtml#gromacs)

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**Author:** ![JieChen](https://avatars.discourse-cdn.com/v4/letter/j/ea5d25/32.png) [@JieChen](https://gromacs.bioexcel.eu/u/JieChen)\
**Post date:** [December 8, 2020, 3:21pm UTC](https://gromacs.bioexcel.eu/t/problem-for-generating-charmm-topol-file-by-cgenff/1226/3 "2020-12-08T15:21:33Z")

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Thanks. I wonder the topol generate by CHARMM36 with CGenFF could be used in CHARMM27 force in Gromacs?

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<div class="post-metadata">

**Author:** ![JieChen](https://avatars.discourse-cdn.com/v4/letter/j/ea5d25/32.png) [@JieChen](https://gromacs.bioexcel.eu/u/JieChen)\
**Post date:** [December 8, 2020, 3:34pm UTC](https://gromacs.bioexcel.eu/t/problem-for-generating-charmm-topol-file-by-cgenff/1226/4 "2020-12-08T15:34:03Z")

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Dear jalemkul,  
I adopt your advise. I downed load the CHARMM36 from the web. But I run the commond I encount the problem as following. I check the forcefield.doc exactly exist in the directory of charm3

 ![屏幕截图 2020-12-08 232935](https://europe1.discourse-cdn.com/flex017/uploads/bioexcel1/original/1X/2758389b7e3768995d777c2b5f3379be8f9049b2.jpeg) 6.ff.

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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:** [December 8, 2020, 3:40pm UTC](https://gromacs.bioexcel.eu/t/problem-for-generating-charmm-topol-file-by-cgenff/1226/5 "2020-12-08T15:40:29Z")

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In principle, CGenFF is compatible with any CHARMM version but our automatic tools are not designed to work with the GROMACS distribution of the old force field. You might be able to make it work, but you’re doing something unintended.

The error you’re getting with CHARMM36 is because you’re not specifying a valid force field directory. Unless you change it, the tarball extracts to charmm36-jul2020.ff, which should be obvious upon listing the files in the directory.

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<div class="post-metadata">

**Author:** ![JieChen](https://avatars.discourse-cdn.com/v4/letter/j/ea5d25/32.png) [@JieChen](https://gromacs.bioexcel.eu/u/JieChen)\
**Post date:** [December 9, 2020, 3:35am UTC](https://gromacs.bioexcel.eu/t/problem-for-generating-charmm-topol-file-by-cgenff/1226/6 "2020-12-09T03:35:52Z")

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I make it. Thanks