# Residue not found in residue topology database

**URL:** <https://gromacs.bioexcel.eu/t/residue-not-found-in-residue-topology-database/12346>\
**Category:** User discussions\
**Created:** [July 9, 2025, 2:34am UTC](https://gromacs.bioexcel.eu/t/residue-not-found-in-residue-topology-database/12346 "2025-07-09T02:34:32Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![XiaoDingdang](https://avatars.discourse-cdn.com/v4/letter/x/a9a28c/32.png) [@XiaoDingdang](https://gromacs.bioexcel.eu/u/XiaoDingdang)\
**Post date:** [July 9, 2025, 2:34am UTC](https://gromacs.bioexcel.eu/t/residue-not-found-in-residue-topology-database/12346/1 "2025-07-09T02:34:32Z")

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GROMACS version:  
GROMACS modification: Yes/No  
Here post your question  
Residue ‘TPO’ not found in residue topology database.May I ask how this should be modified?

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**Author:** ![lmullender](https://avatars.discourse-cdn.com/v4/letter/l/8dc957/32.png) [@lmullender](https://gromacs.bioexcel.eu/u/lmullender)\
**Post date:** [July 14, 2025, 1:27pm UTC](https://gromacs.bioexcel.eu/t/residue-not-found-in-residue-topology-database/12346/2 "2025-07-14T13:27:19Z")

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This is one of the most frequently asked questions, and as such it’s also [answered in the user guide](https://manual.gromacs.org/current/user-guide/run-time-errors.html#residue-xxx-not-found-in-residue-topology-database).

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**Author:** ![XiaoDingdang](https://avatars.discourse-cdn.com/v4/letter/x/a9a28c/32.png) [@XiaoDingdang](https://gromacs.bioexcel.eu/u/XiaoDingdang)\
**Post date:** [July 18, 2025, 7:31am UTC](https://gromacs.bioexcel.eu/t/residue-not-found-in-residue-topology-database/12346/3 "2025-07-18T07:31:23Z")

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Hello, may I ask if you can provide more detailed steps?

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**Author:** ![lmullender](https://avatars.discourse-cdn.com/v4/letter/l/8dc957/32.png) [@lmullender](https://gromacs.bioexcel.eu/u/lmullender)\
**Post date:** [July 18, 2025, 1:51pm UTC](https://gromacs.bioexcel.eu/t/residue-not-found-in-residue-topology-database/12346/4 "2025-07-18T13:51:09Z")

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It’s hardly possible to give more detailed steps than what is already explained at the link above, without knowing what system you’re working with or what you’re trying to achieve. If you’re trying to parametrize e.g. a protein-ligand system, or simply a small organic molecule in water, tools like [CHARMM-GUI’s](https://www.charmm-gui.org/) input generator, [LigParGen](https://zarbi.chem.yale.edu/ligpargen/) or [acpype](https://github.com/alanwilter/acpype) usually come in handy.