# Error triggered by the use of couple-intramol=no

**URL:** <https://gromacs.bioexcel.eu/t/error-triggered-by-the-use-of-couple-intramol-no/5395>\
**Category:** User discussions\
**Tags:** free-energy\
**Created:** [December 9, 2022, 7:13am UTC](https://gromacs.bioexcel.eu/t/error-triggered-by-the-use-of-couple-intramol-no/5395 "2022-12-09T07:13:11Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![ayildirim](https://avatars.discourse-cdn.com/v4/letter/a/919ad9/32.png) [@ayildirim](https://gromacs.bioexcel.eu/u/ayildirim)\
**Post date:** [December 9, 2022, 7:13am UTC](https://gromacs.bioexcel.eu/t/error-triggered-by-the-use-of-couple-intramol-no/5395/1 "2022-12-09T07:13:11Z")

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GROMACS version: 2021  
GROMACS modification: No

Hi,

I am trying to run some free energy simulations using `GROMACS-2021` but I always get the fatal error below. It seems that this is a [bug](https://gitlab.com/gromacs/gromacs/-/issues/3809). Do you know which latter version is stable for free energy calculations?

**Fatal error:**  
There are 7 perturbed non-bonded pair interactions beyond the pair-list cutoff  
of 1.26 nm, which is not supported. This can happen because the system is  
unstable or because intra-molecular interactions at long distances are  
excluded. If the latter is the case, you can try to increase nstlist or rlist  
to avoid this.The error is likely triggered by the use of couple-intramol=no  
and the maximal distance in the decoupled molecule exceeding rlist.

Best,

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**Author:** ![hess](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/hess/32/416_2.png) [@hess](https://gromacs.bioexcel.eu/u/hess)\
**Post date:** [December 9, 2022, 2:26pm UTC](https://gromacs.bioexcel.eu/t/error-triggered-by-the-use-of-couple-intramol-no/5395/2 "2022-12-09T14:26:12Z")

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I would suggest to use 2022.4.