# 'Two replicas have identical temperatures' error during REST2 simulation in GROMACS 2025"

**URL:** <https://gromacs.bioexcel.eu/t/two-replicas-have-identical-temperatures-error-during-rest2-simulation-in-gromacs-2025/13386>\
**Category:** User discussions\
**Created:** [April 15, 2026, 9:05am UTC](https://gromacs.bioexcel.eu/t/two-replicas-have-identical-temperatures-error-during-rest2-simulation-in-gromacs-2025/13386 "2026-04-15T09:05:12Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![jacklu](https://avatars.discourse-cdn.com/v4/letter/j/fbc32d/32.png) [@jacklu](https://gromacs.bioexcel.eu/u/jacklu)\
**Post date:** [April 15, 2026, 9:05am UTC](https://gromacs.bioexcel.eu/t/two-replicas-have-identical-temperatures-error-during-rest2-simulation-in-gromacs-2025/13386/1 "2026-04-15T09:05:12Z")

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GROMACS version:2025.0  
GROMACS modification: No  
“When I **ran** a REST2 calculation using GROMACS with the PLUMED 2.10.0 plugin, I **received** an error: ‘Unknown command-line option -hrex’. After I **removed** the `-hrex` option, it **threw** another error stating that ‘Two replicas have identical temperatures’, **because** the `.mdp` files used to generate the `.tpr` files in different folders were **identical**.” What is the cause of this issue?

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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:** [April 15, 2026, 9:31am UTC](https://gromacs.bioexcel.eu/t/two-replicas-have-identical-temperatures-error-during-rest2-simulation-in-gromacs-2025/13386/2 "2026-04-15T09:31:14Z")

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This looks like a PLUMED issue. But my guess is that you used the MDModule Plumed interface which does not support replica exchange. You need the old, hacky, Plumed interface.