# Problem with calculating the interaction energy between two groups

**URL:** <https://gromacs.bioexcel.eu/t/problem-with-calculating-the-interaction-energy-between-two-groups/3754>\
**Category:** User discussions\
**Tags:** mdp-parameters, mdrun\
**Created:** [March 1, 2022, 7:08am UTC](https://gromacs.bioexcel.eu/t/problem-with-calculating-the-interaction-energy-between-two-groups/3754 "2022-03-01T07:08:41Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![ehsan](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/ehsan/32/1345_2.png) [@ehsan](https://gromacs.bioexcel.eu/u/ehsan)\
**Post date:** [March 1, 2022, 7:08am UTC](https://gromacs.bioexcel.eu/t/problem-with-calculating-the-interaction-energy-between-two-groups/3754/1 "2022-03-01T07:08:42Z")

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GROMACS version: 2021.2  
GROMACS modification: No

I’m following Justin’s tutorial on my system which is a solute and an organic solvent. I want to get the interaction energies between a shell layer of the solvent and the solute. I added these groups to my energygroup of the mdp file and rerun the simulation but I get 0 Coul-SR and vdW-SR for some reason.

If I define all solvents and solute as energygroup it’s all good and not going to be zero. But no matter how big is my shell, I always get 0. Does anybody know what’s wrong with my calculations?

Thanks!

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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:** [March 3, 2022, 1:32pm UTC](https://gromacs.bioexcel.eu/t/problem-with-calculating-the-interaction-energy-between-two-groups/3754/2 "2022-03-03T13:32:54Z")

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This usually happens when the calculations are done on a GPU, which cannot handle energy groups. Make sure to add `-nb cpu` to your `mdrun` command line if you are running the calculations on a machine with a compatible GPU to prevent it from being used.