Problem for generating charmm topol file by CGenFF

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 Sketch jiasuan.mol2 jiasuan.str charmm27.ff " meeting the following problem. How should I do?

You can’t use CHARMM27 with CGenFF. Download the CHARMM36 port from

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

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


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.

I make it. Thanks