# Error in grompp step **URL:** \ **Category:** User discussions\ **Tags:** grompp\ **Created:** [September 17, 2022, 2:40am UTC](https://gromacs.bioexcel.eu/t/error-in-grompp-step/4804 "2022-09-17T02:40:13Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![Kalindu](https://avatars.discourse-cdn.com/v4/letter/k/eada6e/32.png) [@Kalindu](https://gromacs.bioexcel.eu/u/Kalindu)\ **Post date:** [September 17, 2022, 2:40am UTC](https://gromacs.bioexcel.eu/t/error-in-grompp-step/4804/1 "2022-09-17T02:40:14Z")
GROMACS version: 2022 GROMACS modification: No Dear All, I am doing MD simulation of peptides and a ligand. I used ligand reader and modeler in Charmm GUI to generate topology files for the new ligand. When I add it with other peptides and try to run grompp (Gromacs command) the following error was generated. Can anyone suggest to me solve it ? ![Screenshot from 2022-09-17 03-31-45](https://europe1.discourse-cdn.com/flex017/uploads/bioexcel1/original/2X/0/0be7b19e9a6024eaa2e6c7a9a94567db9ada00b5.png) The charmm36.itp file looks like this. ![Screenshot from 2022-09-17 10-39-04](https://europe1.discourse-cdn.com/flex017/uploads/bioexcel1/original/2X/a/a3966daadbd5000fa6c047f25671e4ed7fa67472.png) Thank you ! ---
**Author:** ![alevilla](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/alevilla/32/439_2.png) [@alevilla](https://gromacs.bioexcel.eu/u/alevilla)\ **Post date:** [September 21, 2022, 10:44am UTC](https://gromacs.bioexcel.eu/t/error-in-grompp-step/4804/2 "2022-09-21T10:44:38Z")
Hi, It may be that that force field files/parameters are included in the wrong order in the topology file. Topologies are hierarchical in GROMACS. Here you find more information about [https://manual.gromacs.org/current/reference-manual/topologies/topology-file-formats.html](https://manual.gromacs.org/current/reference-manual/topologies/topology-file-formats.html) \Alessandra