# How to calculate fluctuation dissipation constant (h)

**URL:** <https://gromacs.bioexcel.eu/t/how-to-calculate-fluctuation-dissipation-constant-h/13248>\
**Category:** User discussions\
**Created:** [February 26, 2026, 9:51am UTC](https://gromacs.bioexcel.eu/t/how-to-calculate-fluctuation-dissipation-constant-h/13248 "2026-02-26T09:51:56Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Riya](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/riya/32/4966_2.png) [@Riya](https://gromacs.bioexcel.eu/u/Riya)\
**Post date:** [February 26, 2026, 9:51am UTC](https://gromacs.bioexcel.eu/t/how-to-calculate-fluctuation-dissipation-constant-h/13248/1 "2026-02-26T09:51:56Z")

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![Screenshot_20260224-213851_Drive](https://europe1.discourse-cdn.com/flex017/uploads/bioexcel1/original/2X/8/88c05c3ea242b283a62493ccb58136adb9b10695.jpeg)

GROMACS version: 2025  
I was told to follow a research paper’s protocol and build a 10M urea osmolyte box. I have successfully completed it, but I have a doubt about how to calculate h value, when I am using gmx energy command, there are 2 values for average energy prompted ; Potential energy and total energy. If I am calculating by Potential energy h value is coming around 1.5 while using total energy it is equal to 4. Which one shall i opt for? And also I performed the simulations using CHARMM force field and AMBER and in both cases NVT values are almost same.

Please share your insights. Thank you.