# Epoxide group in OPLS-AA gromacs file

**URL:** <https://gromacs.bioexcel.eu/t/epoxide-group-in-opls-aa-gromacs-file/4173>\
**Category:** User discussions\
**Created:** [May 15, 2022, 4:57pm UTC](https://gromacs.bioexcel.eu/t/epoxide-group-in-opls-aa-gromacs-file/4173 "2022-05-15T16:57:44Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![JakubH](https://avatars.discourse-cdn.com/v4/letter/j/df788c/32.png) [@JakubH](https://gromacs.bioexcel.eu/u/JakubH)\
**Post date:** [May 15, 2022, 4:57pm UTC](https://gromacs.bioexcel.eu/t/epoxide-group-in-opls-aa-gromacs-file/4173/1 "2022-05-15T16:57:44Z")

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GROMACS version: 2020.2  
GROMACS modification: No  
I have a problem. I can’t find parameters for the epoxide group in opls-aa force field files in gromacs files. I want to find all parameters for violaxanthin. [Violaxanthin - Wikipedia](https://en.wikipedia.org/wiki/Violaxanthin) Do these parameters exist or maybe I have to parameterize this molecule by myself? (It would take probably a lot of time) Or maybe I should use a topology generator or use parameters from different force fields? I will be grateful for any advice