# CGenFF problem (versions are not equivalent!) **URL:** \ **Category:** User discussions\ **Created:** [January 15, 2022, 8:09am UTC](https://gromacs.bioexcel.eu/t/cgenff-problem-versions-are-not-equivalent/3484 "2022-01-15T08:09:44Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![serta](https://avatars.discourse-cdn.com/v4/letter/s/65b543/32.png) [@serta](https://gromacs.bioexcel.eu/u/serta)\ **Post date:** [January 15, 2022, 8:09am UTC](https://gromacs.bioexcel.eu/t/cgenff-problem-versions-are-not-equivalent/3484/1 "2022-01-15T08:09:44Z")
GROMACS version: 2020 GROMACS modification: No Hello, I have downloaded the latest charmm36-feb2021.ff port which is having Cgenff version 4.4 in forcefield .doc file . but the .str file generated from the CGENFF program is having cgenff version 4.5. hence showing error. > WARNING: CGenFF versions are not equivalent! I used also charmm36-Jul2021.ff I got the same error > WARNING: CGenFF versions are not equivalent! The CGenFF version in .str file (4.5) The CGenFF version in charmm36-JFeb2021.ff (4.4) The CGenFF version in charmm36-Jul2021.ff (4.6) I used this server [https://cgenff.umaryland.edu/initguess/](https://cgenff.umaryland.edu/initguess/) to generate srt files how to resolve this issue. kindly help ---
**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:** [January 16, 2022, 3:08am UTC](https://gromacs.bioexcel.eu/t/cgenff-problem-versions-are-not-equivalent/3484/2 "2022-01-16T03:08:34Z")
See if `grompp` complains about duplicate parameters. If it does, delete the offending lines from the `.prm` file and use those found in the parent force field. If there’s no conflict, then you can proceed without any problem. Sometimes the CGenFF server lags behind the official force field release; you can contact Alex MacKerell to see if his group can fix that. ---
**Author:** ![Yel21](https://avatars.discourse-cdn.com/v4/letter/y/b2d939/32.png) [@Yel21](https://gromacs.bioexcel.eu/u/Yel21)\ **Post date:** [August 4, 2024, 3:18pm UTC](https://gromacs.bioexcel.eu/t/cgenff-problem-versions-are-not-equivalent/3484/3 "2024-08-04T15:18:31Z")
Hello, Gromacs users. Perhaps you could help me. I wanted to simulate the interactions of antibiotics in the CHARMM36M force field with polymers. The polymers were generated using a polymer builder on a charmm-gui applet. Furthermore, I created the antibiotic topology using a ligand reader and modeler in charmm-gui and [cgennff.com](http://cgennff.com) servers. I compared the difference between the energy components of antibiotics created by the charmm-gui and [cgenff.com](http://cgenff.com) servers and obtained the difference between all the components of force fields between the topologies parameterized by both charmm-gui and [cgenff.com](http://cgenff.com) servers. When I began to compare the versions of the cgenff force field, I found that both servers used cgenff version 4.6. However, the [Cgenff.com](http://Cgenff.com) server uses a much newer version of the program version 4.0 by Jun 2024 than the Charmm-Gui, which was the Cgenff program version 2.5.1 by August 2021. In addition, the charmm36 force field version 2018 November was added to the cgenff topology generated by the [cgenff.com](http://cgenff.com) server. I could not determine which version of the charmm36 force field was used for parametrization of the polymers and antibiotics when I used a polymer builder and ligand reader applets in charmm-gui. Could I combine the topologies of polymers generated using charmm-gui with the topology of antibiotics generated using the [cgenff.com](http://cgenff.com) server, or should I use the topology of antibiotics generated by a ligand reader and modeler applet in charmm-gui? Could I change the older version of the charmm36 force filed from November 2018 to the latest version from July 2022?