# Hamiltonian replica exchange

**URL:** <https://gromacs.bioexcel.eu/t/hamiltonian-replica-exchange/463>\
**Category:** User discussions\
**Created:** [July 10, 2020, 11:05am UTC](https://gromacs.bioexcel.eu/t/hamiltonian-replica-exchange/463 "2020-07-10T11:05:25Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![siddiqh](https://avatars.discourse-cdn.com/v4/letter/s/ecccb3/32.png) [@siddiqh](https://gromacs.bioexcel.eu/u/siddiqh)\
**Post date:** [July 10, 2020, 11:05am UTC](https://gromacs.bioexcel.eu/t/hamiltonian-replica-exchange/463/1 "2020-07-10T11:05:25Z")

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GROMACS version:  
GROMACS modification: Yes/No  
Here post your question  
Is Hamiltonian replica exchange implemented in all gromacs version, and if I want to run Hamiltonian replica exchange only using gromacs without plumed is it possible?

Thanks

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**Author:** ![Dr\_DBW](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/dr_dbw/32/42_2.png) [@Dr\_DBW](https://gromacs.bioexcel.eu/u/Dr_DBW)\
**Post date:** [July 13, 2020, 11:12am UTC](https://gromacs.bioexcel.eu/t/hamiltonian-replica-exchange/463/2 "2020-07-13T11:12:01Z")

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As of yet, no.

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**Author:** ![DamianoBuratto](https://avatars.discourse-cdn.com/v4/letter/d/8e8cbc/32.png) [@DamianoBuratto](https://gromacs.bioexcel.eu/u/DamianoBuratto)\
**Post date:** [February 25, 2021, 6:15am UTC](https://gromacs.bioexcel.eu/t/hamiltonian-replica-exchange/463/3 "2021-02-25T06:15:31Z")

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Dear all,

I am trying to compute a binding energy using alchemical transformation and following this tutorial  
[http://www.alchemistry.org/wiki/Absolute\_Binding\_Free\_Energy\_-\_Gromacs\_2016](http://www.alchemistry.org/wiki/Absolute_Binding_Free_Energy_-_Gromacs_2016)  
I have found that the use of Hamiltonian Replica Exchange (HREX) can considerably improve the sampling. The command line they suggest (on GROMACS2016) is:

> mdrun -multidir lambda.\*/PROD/ -s prod.tpr -deffnm prod -replex 1000 -nex 1000000

and does not include plumed. I tried to run it on my system and I am getting errors that I cannot solve. So I was wondering: is this wrong or is actually possible to run HREX without plumed?

Thank you very much for your time,  
Damiano