# Forcefield to simulate RNA molecules containing modifications with GROMACS and amber ff

**URL:** <https://gromacs.bioexcel.eu/t/forcefield-to-simulate-rna-molecules-containing-modifications-with-gromacs-and-amber-ff/5986>\
**Category:** User discussions\
**Tags:** forcefield, simulation-setup\
**Created:** [March 16, 2023, 9:14am UTC](https://gromacs.bioexcel.eu/t/forcefield-to-simulate-rna-molecules-containing-modifications-with-gromacs-and-amber-ff/5986 "2023-03-16T09:14:41Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Angana](https://avatars.discourse-cdn.com/v4/letter/a/bbce88/32.png) [@Angana](https://gromacs.bioexcel.eu/u/Angana)\
**Post date:** [March 16, 2023, 9:14am UTC](https://gromacs.bioexcel.eu/t/forcefield-to-simulate-rna-molecules-containing-modifications-with-gromacs-and-amber-ff/5986/1 "2023-03-16T09:14:41Z")

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GROMACS version: version 2023

I am planning to do simulations of RNA molecules that contain modifications such as PSU, etc. I understand that for RNA simulations I should use [amber14sb\_OL21.ff](https://fch.upol.cz/ff_ol/amber14sb_OL21.ff.tar.gz) package as the forcefield. And this package is gromacs compatible. However, in-addition, I also need to use [https://pubs.acs.org/doi/abs/10.1021/ct600329w](https://pubs.acs.org/doi/abs/10.1021/ct600329w) this forcefield for modifcations. Is there a chance I can get this forcefield in gromacs compatible mode? Or any other suggestion is also welcome.

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**Author:** ![rupa](https://avatars.discourse-cdn.com/v4/letter/r/51bf81/32.png) [@rupa](https://gromacs.bioexcel.eu/u/rupa)\
**Post date:** [June 20, 2025, 9:18am UTC](https://gromacs.bioexcel.eu/t/forcefield-to-simulate-rna-molecules-containing-modifications-with-gromacs-and-amber-ff/5986/2 "2025-06-20T09:18:21Z")

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Do you able to do it?

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**Author:** ![rupa](https://avatars.discourse-cdn.com/v4/letter/r/51bf81/32.png) [@rupa](https://gromacs.bioexcel.eu/u/rupa)\
**Post date:** [June 20, 2025, 9:19am UTC](https://gromacs.bioexcel.eu/t/forcefield-to-simulate-rna-molecules-containing-modifications-with-gromacs-and-amber-ff/5986/3 "2025-06-20T09:19:27Z")

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i am facing some problems while using OL3 forcefeild in amber as tleap is not able to run it cant recognize Cl- and Phosphate ions