# Should all bonds be constrained in lipid bilayer simulations with CHARMM36?

**URL:** <https://gromacs.bioexcel.eu/t/should-all-bonds-be-constrained-in-lipid-bilayer-simulations-with-charmm36/7070>\
**Category:** User discussions\
**Tags:** mdp-parameters, mdrun, constraint-algorithms\
**Created:** [August 23, 2023, 9:14pm UTC](https://gromacs.bioexcel.eu/t/should-all-bonds-be-constrained-in-lipid-bilayer-simulations-with-charmm36/7070 "2023-08-23T21:14:21Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![RomanS](https://avatars.discourse-cdn.com/v4/letter/r/5e9695/32.png) [@RomanS](https://gromacs.bioexcel.eu/u/RomanS)\
**Post date:** [August 23, 2023, 9:14pm UTC](https://gromacs.bioexcel.eu/t/should-all-bonds-be-constrained-in-lipid-bilayer-simulations-with-charmm36/7070/1 "2023-08-23T21:14:21Z")

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GROMACS version: 2023  
GROMACS modification: Yes

According to the documentation, only h-bonds should be constrained with CHARMM36. Does that apply to simulations of lipid bilayers, or should all bonds be constrained?

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**Author:** ![jalemkul](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/jalemkul/32/18_2.png) [@jalemkul](https://gromacs.bioexcel.eu/u/jalemkul)\
**Post date:** [August 23, 2023, 9:27pm UTC](https://gromacs.bioexcel.eu/t/should-all-bonds-be-constrained-in-lipid-bilayer-simulations-with-charmm36/7070/2 "2023-08-23T21:27:12Z")

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Constraining bonds to H atoms is appropriate for any simulation with the CHARMM force field, irrespective of the contents of the system. Do not constrain all bonds with CHARMM.