# Problem during hbond calculation per water molecule using gmx hbond

**URL:** <https://gromacs.bioexcel.eu/t/problem-during-hbond-calculation-per-water-molecule-using-gmx-hbond/4632>\
**Category:** User discussions\
**Created:** [August 17, 2022, 9:15am UTC](https://gromacs.bioexcel.eu/t/problem-during-hbond-calculation-per-water-molecule-using-gmx-hbond/4632 "2022-08-17T09:15:40Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Sourav7](https://avatars.discourse-cdn.com/v4/letter/s/ba9def/32.png) [@Sourav7](https://gromacs.bioexcel.eu/u/Sourav7)\
**Post date:** [August 17, 2022, 9:15am UTC](https://gromacs.bioexcel.eu/t/problem-during-hbond-calculation-per-water-molecule-using-gmx-hbond/4632/1 "2022-08-17T09:15:40Z")

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GROMACS version:  
GROMACS modification: Yes/No  
Here post your question  
I am calculating h bond of SPC/E water using gmx hbond tool. I got approximate 1.8 hydrogen bond per water molecule. But one water molecule can form 4 hbond. I think they calculate hbond between O atom of one water to the H atom of others. But they didn’t consider the two H atoms of one water to the O atom of other water molecule. How can we solve it. Please help.

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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 18, 2022, 10:56am UTC](https://gromacs.bioexcel.eu/t/problem-during-hbond-calculation-per-water-molecule-using-gmx-hbond/4632/2 "2022-08-18T10:56:20Z")

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The default behavior is to merge equivalent hydrogens (consider them equivalent), so if you want to disable this, use `-nomerge`.

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**Author:** ![TijinSaji](https://avatars.discourse-cdn.com/v4/letter/t/6f9a4e/32.png) [@TijinSaji](https://gromacs.bioexcel.eu/u/TijinSaji)\
**Post date:** [May 12, 2023, 9:03am UTC](https://gromacs.bioexcel.eu/t/problem-during-hbond-calculation-per-water-molecule-using-gmx-hbond/4632/3 "2023-05-12T09:03:57Z")

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I am facing the same issue.  
I tried calculating the average number of Hydrogen bonds (HBs) per SPC water molecule with `gmx hbond` with `-nomerge`. However, I still get around 1.8 HBs per water molecule. What could be the problem?

GROMACS version: 2022.4