# Very custom constraints issue **URL:** \ **Category:** User discussions\ **Tags:** grompp\ **Created:** [June 1, 2022, 8:38pm UTC](https://gromacs.bioexcel.eu/t/very-custom-constraints-issue/4249 "2022-06-01T20:38:59Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![dkonstan](https://avatars.discourse-cdn.com/v4/letter/d/87869e/32.png) [@dkonstan](https://gromacs.bioexcel.eu/u/dkonstan)\ **Post date:** [June 1, 2022, 8:38pm UTC](https://gromacs.bioexcel.eu/t/very-custom-constraints-issue/4249/1 "2022-06-01T20:38:59Z")
GROMACS version: 2022 GROMACS modification: No I want to simulate a system containing a protein, water, and some solutes (urea and TMAO). I have the following constraints (for LINCS) situation: the protein should have only h-bonds constrained, the urea should be totally constrained, while the TMAO should be totally unconstrained (even C-H bonds). Is there a way I can do this without manually putting constraints in the [constraints] section of the topology for all the species? Thank you! Dan ---
**Author:** ![hess](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/hess/32/416_2.png) [@hess](https://gromacs.bioexcel.eu/u/hess)\ **Post date:** [June 3, 2022, 9:15am UTC](https://gromacs.bioexcel.eu/t/very-custom-constraints-issue/4249/2 "2022-06-03T09:15:01Z")
No, unfortunately there is no other way of doing this. ---
**Author:** ![hess](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/hess/32/416_2.png) [@hess](https://gromacs.bioexcel.eu/u/hess)\ **Post date:** [June 3, 2022, 9:19am UTC](https://gromacs.bioexcel.eu/t/very-custom-constraints-issue/4249/3 "2022-06-03T09:19:17Z")
Actually, you can use a trick to be able to specify h-bonds constraints, so don’t need to change anything for the protein, which I assume would be the most work. You change TMAO to use (H-)bonds type 6 instead of 1, so these are not converted to constraints by grompp. But then you need to manually set all exclusions in TMAO.