# Gmx hbond - contact option

**URL:** <https://gromacs.bioexcel.eu/t/gmx-hbond-contact-option/4220>\
**Category:** User discussions\
**Tags:** analysis-tools\
**Created:** [May 26, 2022, 1:04pm UTC](https://gromacs.bioexcel.eu/t/gmx-hbond-contact-option/4220 "2022-05-26T13:04:07Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Anna13](https://avatars.discourse-cdn.com/v4/letter/a/e47774/32.png) [@Anna13](https://gromacs.bioexcel.eu/u/Anna13)\
**Post date:** [May 26, 2022, 1:04pm UTC](https://gromacs.bioexcel.eu/t/gmx-hbond-contact-option/4220/1 "2022-05-26T13:04:07Z")

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GROMACS version: 2020.6  
GROMACS modification: No

Hi everyone.

We want to have a list of all the contacts between two proteins within a 0.5 nm cutoff.

If we want to use the -contact option of gmx hbond we should change the -r flag (0.5 instead of the 0.35 default) and not use the flag -r2, are we right?

In other words, if we are interested in all kind of contacts, leaving -r = 0.35 would be meaningless because this cutoff is specific for h-bonds interaction…

This is what we understood.  
we are using this command:

gmx hbond -s .tpr -f .xtc -n .ndx -g hbond\_ref.log -hbn hbindex\_ref.ndx -contact -r 0.5

any comment would be helpful.  
thank you!

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<div class="post-metadata">

**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:** [May 31, 2022, 2:41am UTC](https://gromacs.bioexcel.eu/t/gmx-hbond-contact-option/4220/2 "2022-05-31T02:41:03Z")

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The better approach to counting generic contacts is `gmx mindist -on`.