# Error during umbrella sampling

**URL:** <https://gromacs.bioexcel.eu/t/error-during-umbrella-sampling/6896>\
**Category:** User discussions\
**Created:** [July 27, 2023, 9:05am UTC](https://gromacs.bioexcel.eu/t/error-during-umbrella-sampling/6896 "2023-07-27T09:05:22Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![mayankbisht184](https://avatars.discourse-cdn.com/v4/letter/m/e5b9ba/32.png) [@mayankbisht184](https://gromacs.bioexcel.eu/u/mayankbisht184)\
**Post date:** [July 27, 2023, 9:05am UTC](https://gromacs.bioexcel.eu/t/error-during-umbrella-sampling/6896/1 "2023-07-27T09:05:22Z")

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GROMACS version:2020.1-Ubuntu-2020.1-1  
GROMACS modification: Yes/No  
Here post your question  
During umbrella sampling:  
Distance between pull groups 1 and 2 (2.014074 nm) is larger than 0.49 times  
the box size (1.568000).  
How to resolve this error?

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**Author:** ![Karis](https://avatars.discourse-cdn.com/v4/letter/k/ed8c4c/32.png) [@Karis](https://gromacs.bioexcel.eu/u/Karis)\
**Post date:** [July 27, 2023, 10:08am UTC](https://gromacs.bioexcel.eu/t/error-during-umbrella-sampling/6896/2 "2023-07-27T10:08:01Z")

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You need to make sure the length of the box in the direction you’re pulling is always larger than twice the distance between your pull groups. For example, if you know pulling groups 1 and 2 will reach a maximum of 4 nm apart, the box along that length must be at least 8 nm long