# Hydrogen bond definition

**URL:** <https://gromacs.bioexcel.eu/t/hydrogen-bond-definition/1841>\
**Category:** User discussions\
**Created:** [March 27, 2021, 7:26pm UTC](https://gromacs.bioexcel.eu/t/hydrogen-bond-definition/1841 "2021-03-27T19:26:26Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![peter.mawanga](https://avatars.discourse-cdn.com/v4/letter/p/ccd318/32.png) [@peter.mawanga](https://gromacs.bioexcel.eu/u/peter.mawanga)\
**Post date:** [March 27, 2021, 7:26pm UTC](https://gromacs.bioexcel.eu/t/hydrogen-bond-definition/1841/1 "2021-03-27T19:26:26Z")

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GROMACS version: 2019.5  
GROMACS modification: No

Hello everyone,

I noticed that the hydrogen bond angle is set to 30 degrees by default for the `gmx hbond` analysis tool. But I would like to know the reason for selecting this particular cut off.

Could someone please share the associated literature where this cutoff has been discussed? Thanks a lot!

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**Author:** ![cloudella](https://avatars.discourse-cdn.com/v4/letter/c/7ea924/32.png) [@cloudella](https://gromacs.bioexcel.eu/u/cloudella)\
**Post date:** [March 30, 2023, 9:01am UTC](https://gromacs.bioexcel.eu/t/hydrogen-bond-definition/1841/2 "2023-03-30T09:01:11Z")

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Hi there!  
I am asking myself the exact same question right now, as in the literature I can only find reasonable cutoff angles around 120 degrees. Have you found out, why here it is set at 30 and if this makes sense or one should change it?