# Force Field parameters for ATP/ADP/GTP/GDP with OPLS?

**URL:** <https://gromacs.bioexcel.eu/t/force-field-parameters-for-atp-adp-gtp-gdp-with-opls/261>\
**Category:** User discussions\
**Created:** [June 7, 2020, 8:36pm UTC](https://gromacs.bioexcel.eu/t/force-field-parameters-for-atp-adp-gtp-gdp-with-opls/261 "2020-06-07T20:36:40Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![mick](https://avatars.discourse-cdn.com/v4/letter/m/f04885/32.png) [@mick](https://gromacs.bioexcel.eu/u/mick)\
**Post date:** [June 7, 2020, 8:36pm UTC](https://gromacs.bioexcel.eu/t/force-field-parameters-for-atp-adp-gtp-gdp-with-opls/261/1 "2020-06-07T20:36:40Z")

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GROMACS version: 2020  
GROMACS modification: No

I’ve been running a number of simulations with OPLS using the LigParGen server from Jorgensen’s lab for ligands, but I’ve noticed that OPLS has separate papers on parameters for the common ADP/ATP/GTP/GDP molecules that may be more accurate. Unfortunately, I’ve not come across any GROMACS formatted versions of these molecules.

Before I start down the path of manually converting, I was wondering if anyone else has done this before or if anyone has a good way of converting CHARMM formatted param/top files (which are available from Jorgensen’s webpage) to gromacs itp (or ideally both itp formats and gromacs residue topology file entries).

Thanks in advance

-Micholas