# Gmx hbond autocorrelation function

**URL:** <https://gromacs.bioexcel.eu/t/gmx-hbond-autocorrelation-function/11634>\
**Category:** User discussions\
**Created:** [February 26, 2025, 8:13pm UTC](https://gromacs.bioexcel.eu/t/gmx-hbond-autocorrelation-function/11634 "2025-02-26T20:13:02Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Julian](https://avatars.discourse-cdn.com/v4/letter/j/74df32/32.png) [@Julian](https://gromacs.bioexcel.eu/u/Julian)\
**Post date:** [February 26, 2025, 8:13pm UTC](https://gromacs.bioexcel.eu/t/gmx-hbond-autocorrelation-function/11634/1 "2025-02-26T20:13:02Z")

</div>

GROMACS version: 2023.3  
GROMACS modification: Yes/No  
Hello,

I am running gmx hbond and am wondering how to have it so that the autocorrelation function is calculated over 200 picoseconds. It seems that the arguemnts -acflen does not work or I am not using it properly. I understand that the default is half of the given timeframe, how could I make it whole, for example. Thank you for your time.

gmx hbond -f …/…/…/new4.xtc -s …/…/…/hd\_1i1f.tpr -num test3.xvg -b 0 -e 200 -n res\_water1.ndx -P 1 -temp 310 -ac acf\_test3.xvg