# How not to use defaults **URL:** \ **Category:** User discussions\ **Created:** [March 27, 2025, 7:09pm UTC](https://gromacs.bioexcel.eu/t/how-not-to-use-defaults/11823 "2025-03-27T19:09:03Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![Eliza](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/eliza/32/4492_2.png) [@Eliza](https://gromacs.bioexcel.eu/u/Eliza)\ **Post date:** [March 27, 2025, 7:09pm UTC](https://gromacs.bioexcel.eu/t/how-not-to-use-defaults/11823/1 "2025-03-27T19:09:03Z")
GROMACS version: 2019.6 GROMACS modification: Yes/No Here post your question I am trying to use 2 FFs: Buck.ham and LJ when I use the defaults for Buckham it does not get the LJ pairtypes. Can I exclude the defaults or is there a way to set the defaults as I want them to run? this is the B.ham defaults: [defaults] ; nbfunc comb-rule gen-pairs fudgeLJ fudgeQQ 2 2 no 0.5 0.833333 and, this is the LJ defaults: [defaults] ; nbfunc comb-rule gen-pairs fudgeLJ fudgeQQ 1 2 no 0.5 0.833333 Thanks ---
**Author:** ![obZehn](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/obzehn/32/2629_2.png) [@obZehn](https://gromacs.bioexcel.eu/u/obZehn)\ **Post date:** [March 28, 2025, 9:18am UTC](https://gromacs.bioexcel.eu/t/how-not-to-use-defaults/11823/2 "2025-03-28T09:18:17Z")
Hi @Eliza i) I am pretty sure you can’t mix Buckingham and Lennard-Jones in GROMACS, you have to pick one of the two; ii) Buckingham is not supported in GROMACS since at least 2019.