# How to select conformation with the lowest free energy?

**URL:** <https://gromacs.bioexcel.eu/t/how-to-select-conformation-with-the-lowest-free-energy/1463>\
**Category:** User discussions\
**Created:** [January 18, 2021, 7:17pm UTC](https://gromacs.bioexcel.eu/t/how-to-select-conformation-with-the-lowest-free-energy/1463 "2021-01-18T19:17:08Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![sam](https://avatars.discourse-cdn.com/v4/letter/s/5f9b8f/32.png) [@sam](https://gromacs.bioexcel.eu/u/sam)\
**Post date:** [January 18, 2021, 7:17pm UTC](https://gromacs.bioexcel.eu/t/how-to-select-conformation-with-the-lowest-free-energy/1463/1 "2021-01-18T19:17:08Z")

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GROMACS version: 2020.4  
After finishing my single peptide simulation in water i applied g cluster command to find the size of the most populated conformations so how to select the best conformation with the lowest free energy ?  
I cannot find free energy choice in using g energy command

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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:** [January 18, 2021, 7:34pm UTC](https://gromacs.bioexcel.eu/t/how-to-select-conformation-with-the-lowest-free-energy/1463/2 "2021-01-18T19:34:07Z")

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That would require some kind of MM/PBSA calculation to compute a configurational free energy. There’s no tool in (official) GROMACS that does that.

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**Author:** ![sam](https://avatars.discourse-cdn.com/v4/letter/s/5f9b8f/32.png) [@sam](https://gromacs.bioexcel.eu/u/sam)\
**Post date:** [January 18, 2021, 7:57pm UTC](https://gromacs.bioexcel.eu/t/how-to-select-conformation-with-the-lowest-free-energy/1463/3 "2021-01-18T19:57:19Z")

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Thanks for replying So is it possible to use free energy surface for rmsd and rgy to find the Lowest energy of conformation

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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:** [January 18, 2021, 9:34pm UTC](https://gromacs.bioexcel.eu/t/how-to-select-conformation-with-the-lowest-free-energy/1463/4 "2021-01-18T21:34:28Z")

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Boltzmann weighting of any relevant quantities is an approach that is commonly used, yes.

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**Author:** ![sam](https://avatars.discourse-cdn.com/v4/letter/s/5f9b8f/32.png) [@sam](https://gromacs.bioexcel.eu/u/sam)\
**Post date:** [January 19, 2021, 12:45am UTC](https://gromacs.bioexcel.eu/t/how-to-select-conformation-with-the-lowest-free-energy/1463/5 "2021-01-19T00:45:25Z")

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Thanks for replying and helping