# Free energy calculations, Langevin dynamics

**URL:** <https://gromacs.bioexcel.eu/t/free-energy-calculations-langevin-dynamics/2162>\
**Category:** User discussions\
**Created:** [May 13, 2021, 10:21am UTC](https://gromacs.bioexcel.eu/t/free-energy-calculations-langevin-dynamics/2162 "2021-05-13T10:21:23Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![dimozino](https://avatars.discourse-cdn.com/v4/letter/d/f19dbf/32.png) [@dimozino](https://gromacs.bioexcel.eu/u/dimozino)\
**Post date:** [May 13, 2021, 10:21am UTC](https://gromacs.bioexcel.eu/t/free-energy-calculations-langevin-dynamics/2162/1 "2021-05-13T10:21:23Z")

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GROMACS version: 2019  
GROMACS modification: No

Dear all,

In free energy calculations, we use Langevin integrator.  
However, can we use md integrator with some other thermostat? Is there a fundamental problem which prevents using other kinds of thermostats for free energy calculations?

Best regards,  
Dmitrii

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**Author:** ![hess](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/hess/32/416_2.png) [@hess](https://gromacs.bioexcel.eu/u/hess)\
**Post date:** [May 14, 2021, 12:23pm UTC](https://gromacs.bioexcel.eu/t/free-energy-calculations-langevin-dynamics/2162/2 "2021-05-14T12:23:54Z")

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Yes, there is a fundamental problem when one decouples a molecule or degrees of freedom. Then thermostat is required that thermalizes all degrees of freedom individually. An An integrator is one of there, but an Andersen thermostat might also work.

When no degrees of freedom are decoupled, you can use any thermostat.

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**Author:** ![dimozino](https://avatars.discourse-cdn.com/v4/letter/d/f19dbf/32.png) [@dimozino](https://gromacs.bioexcel.eu/u/dimozino)\
**Post date:** [May 15, 2021, 10:29am UTC](https://gromacs.bioexcel.eu/t/free-energy-calculations-langevin-dynamics/2162/3 "2021-05-15T10:29:39Z")

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Thank you very much for your answer!