# Getting fluctuations in temperature during npt run

**URL:** <https://gromacs.bioexcel.eu/t/getting-fluctuations-in-temperature-during-npt-run/2700>\
**Category:** User discussions\
**Tags:** forcefield, mdrun, analysis-tools\
**Created:** [August 19, 2021, 10:47am UTC](https://gromacs.bioexcel.eu/t/getting-fluctuations-in-temperature-during-npt-run/2700 "2021-08-19T10:47:30Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![sikisipra](https://avatars.discourse-cdn.com/v4/letter/s/e9a140/32.png) [@sikisipra](https://gromacs.bioexcel.eu/u/sikisipra)\
**Post date:** [August 19, 2021, 10:47am UTC](https://gromacs.bioexcel.eu/t/getting-fluctuations-in-temperature-during-npt-run/2700/1 "2021-08-19T10:47:30Z")

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GROMACS version:2021.2  
GROMACS modification: Yes/No  
Dear users,  
I am simulating a polymer using gromos forcefield parameters. After minimization, i ran canonical ensemble (NVT). During NVT i got a temperature fluctuation of ± 5K about its average value which is 425 K. Now when I switch to the NPT ensemble, my temperature fluctioans are increasing. During NPT temperature is fluctuating ±50 K about its average value which is 425. I did ibserve the system for 2ns.  
Please help me to minimize the temperature fluctuations of my system.  
 ![tempearture_npt](https://europe1.discourse-cdn.com/flex017/uploads/bioexcel1/original/2X/c/ca312dd213ede42e75915edd790f78e847edf86d.jpeg)

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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:** [August 19, 2021, 2:14pm UTC](https://gromacs.bioexcel.eu/t/getting-fluctuations-in-temperature-during-npt-run/2700/2 "2021-08-19T14:14:26Z")

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What thermostat settings did you use in each phase of the simulations? Methods like V-rescale have intrinsically much smaller fluctuations than, e.g. Nosé-Hoover, and you can modulate the magnitude of fluctuations with τT for both.

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**Author:** ![sikisipra](https://avatars.discourse-cdn.com/v4/letter/s/e9a140/32.png) [@sikisipra](https://gromacs.bioexcel.eu/u/sikisipra)\
**Post date:** [August 21, 2021, 3:29am UTC](https://gromacs.bioexcel.eu/t/getting-fluctuations-in-temperature-during-npt-run/2700/3 "2021-08-21T03:29:31Z")

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Thank you for your reply. I have changed the thermostat from Nose-Hoover to V-rescale and it worked. Now the temperature fluctuation is less.