# Residue mapped into topology database but atom name not found in file?

**URL:** <https://gromacs.bioexcel.eu/t/residue-mapped-into-topology-database-but-atom-name-not-found-in-file/3675>\
**Category:** User discussions\
**Created:** [February 15, 2022, 6:28pm UTC](https://gromacs.bioexcel.eu/t/residue-mapped-into-topology-database-but-atom-name-not-found-in-file/3675 "2022-02-15T18:28:25Z")\
**Posts on this page:** 1\
**Showing post:** 11

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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:** [March 26, 2023, 5:11pm UTC](https://gromacs.bioexcel.eu/t/residue-mapped-into-topology-database-but-atom-name-not-found-in-file/3675/11 "2023-03-26T17:11:25Z")

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> [@amei](#):
>
> Residue 47 named TRP of a molecule in the input file was mapped  
> to an entry in the topology database, but the atom CH2 used in  
> that entry is not found in the input file. Perhaps your atom  
> and/or residue naming needs to be fixed.

Either your atom is named incorrectly in the input coordinate file or it’s missing. In the event of the former, rename it to CH2. If the latter, you need to model in any missing atoms using software outside of GROMACS before trying to run `pdb2gmx`. This is an extremely common error.

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