# Where do I find the amber99sb.ff forcefield file?

**URL:** <https://gromacs.bioexcel.eu/t/where-do-i-find-the-amber99sb-ff-forcefield-file/11524>\
**Category:** User discussions\
**Created:** [February 11, 2025, 8:12pm UTC](https://gromacs.bioexcel.eu/t/where-do-i-find-the-amber99sb-ff-forcefield-file/11524 "2025-02-11T20:12:53Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![ryanm](https://avatars.discourse-cdn.com/v4/letter/r/85f322/32.png) [@ryanm](https://gromacs.bioexcel.eu/u/ryanm)\
**Post date:** [February 11, 2025, 8:12pm UTC](https://gromacs.bioexcel.eu/t/where-do-i-find-the-amber99sb-ff-forcefield-file/11524/1 "2025-02-11T20:12:53Z")

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GROMACS version: 2021.4  
GROMACS modification: Yes/No  
Here post your question:  
I am using gmx x2top to generate a topology file from a gro file. It doesn’t recognize some of the water and Cl atoms in the gro file. This gro file has a metal site, so that is why I want to use amber99sb.ff force-field. I think I need the amber99sb.ff force-field file or directory to manually specified the type of ions and water associated with the amber99sb.ff force-field.

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**Author:** ![Miyssa](https://avatars.discourse-cdn.com/v4/letter/m/e47774/32.png) [@Miyssa](https://gromacs.bioexcel.eu/u/Miyssa)\
**Post date:** [February 12, 2025, 12:54am UTC](https://gromacs.bioexcel.eu/t/where-do-i-find-the-amber99sb-ff-forcefield-file/11524/2 "2025-02-12T00:54:07Z")

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Hi, you can download AmberTools ([AmberTools24](https://ambermd.org/AmberTools.php)) and use xleap to generate the topology using the Amber force field of your choice. Then, you can convert the files into GROMACS format.  
Also, I think it’s better to update your GROMACS version. The 2021 release is old, go for 2024.5 instead.  
All the good luck.