# Fatal Error: Residue Not Found in the Residue Topology Database

**URL:** <https://gromacs.bioexcel.eu/t/fatal-error-residue-not-found-in-the-residue-topology-database/6215>\
**Category:** User discussions\
**Tags:** forcefield\
**Created:** [April 17, 2023, 11:58am UTC](https://gromacs.bioexcel.eu/t/fatal-error-residue-not-found-in-the-residue-topology-database/6215 "2023-04-17T11:58:54Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Abhishek\_cupb](https://avatars.discourse-cdn.com/v4/letter/a/958977/32.png) [@Abhishek\_cupb](https://gromacs.bioexcel.eu/u/Abhishek_cupb)\
**Post date:** [April 17, 2023, 11:58am UTC](https://gromacs.bioexcel.eu/t/fatal-error-residue-not-found-in-the-residue-topology-database/6215/1 "2023-04-17T11:58:54Z")

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GROMACS version: 2023  
GROMACS modification: No  
I have a PDB file of Graphene oxide nanosheet. When I am using the pdb2gmx command I am getting an error of residue not found. Can you please help?

 ![Screenshot from 2023-04-17 17-27-36](https://europe1.discourse-cdn.com/flex017/uploads/bioexcel1/original/2X/3/3e1ba5dcccadcfd67609065407d8535c96d8a998.png)

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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:** [April 17, 2023, 12:45pm UTC](https://gromacs.bioexcel.eu/t/fatal-error-residue-not-found-in-the-residue-topology-database/6215/2 "2023-04-17T12:45:41Z")

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Materials like graphene and related species are best built with `x2top`, as `pdb2gmx` is really only intended to build linear polymers of known residue composition. There is no way it can know what what graphene oxide is. You will need to define atomic properties in your force field’s `.n2t` file for `x2top` to work.

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**Author:** ![Abhishek\_cupb](https://avatars.discourse-cdn.com/v4/letter/a/958977/32.png) [@Abhishek\_cupb](https://gromacs.bioexcel.eu/u/Abhishek_cupb)\
**Post date:** [April 17, 2023, 1:12pm UTC](https://gromacs.bioexcel.eu/t/fatal-error-residue-not-found-in-the-residue-topology-database/6215/3 "2023-04-17T13:12:40Z")

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Thank you Sir. I will go through the .n2t file.