# Error in grompp

**URL:** <https://gromacs.bioexcel.eu/t/error-in-grompp/2145>\
**Category:** User discussions\
**Tags:** forcefield, analysis-tools\
**Created:** [May 11, 2021, 12:06pm UTC](https://gromacs.bioexcel.eu/t/error-in-grompp/2145 "2021-05-11T12:06:05Z")\
**Posts on this page:** 1\
**Showing post:** 2

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**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:** [May 14, 2021, 9:33am UTC](https://gromacs.bioexcel.eu/t/error-in-grompp/2145/2 "2021-05-14T09:33:49Z")

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Hi,

The error just say that parameters for dihedral angles are missing in your force field implementation. Propably the dihedral angles are defined in the itp file, but gmx pdb2gmx does not find the corresponding values in the ffbond.itp (force field file)

See other topics on this topic in the form (for example)

> [@How to use output from PRODRG](https://gromacs.bioexcel.eu/t/how-to-use-output-from-prodrg/436):
>
> GROMACS version: 2018.3 GROMACS modification: No I am studying protein-ligand interactions, and my question has two parts which may be related: To get an .itp file for my ligand, I submitted its .pdb file to PRODRG server (since I am using Gromos forcefield), and I guess I should use DRGGMX.pdb and DRGGMX.itp. How do I use the output files from PRODRG for Gromacs simulations? I did editconfig to convert the DRGGMX.pdb into .gro, and then copied the content into the protein.gro Then I adde…

Best regards  
Alessandra

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