# PC and gromacs requirements for REMD

**URL:** <https://gromacs.bioexcel.eu/t/pc-and-gromacs-requirements-for-remd/5438>\
**Category:** User discussions\
**Created:** [December 15, 2022, 10:50pm UTC](https://gromacs.bioexcel.eu/t/pc-and-gromacs-requirements-for-remd/5438 "2022-12-15T22:50:21Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![Neena](https://avatars.discourse-cdn.com/v4/letter/n/bc79bd/32.png) [@Neena](https://gromacs.bioexcel.eu/u/Neena)\
**Post date:** [December 15, 2022, 10:50pm UTC](https://gromacs.bioexcel.eu/t/pc-and-gromacs-requirements-for-remd/5438/1 "2022-12-15T22:50:21Z")

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GROMACS version: 2021.3

Hello Gromacs users,

For running 16 replicas REMD on gromacs, what are the minimum system requirements and gromacs compilation requirements needed? My system currently has 6 processors.

Thank you,  
Neena

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**Author:** ![alevilla](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/alevilla/32/439_2.png) [@alevilla](https://gromacs.bioexcel.eu/u/alevilla)\
**Post date:** [December 19, 2022, 1:43pm UTC](https://gromacs.bioexcel.eu/t/pc-and-gromacs-requirements-for-remd/5438/2 "2022-12-19T13:43:44Z")

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HI,  
here you find the GROMACS 2022 installation prerequisites:  
[https://manual.gromacs.org/documentation/current/install-guide/index.html#prerequisites](https://manual.gromacs.org/documentation/current/install-guide/index.html#prerequisites)  
\Alessandra

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**Author:** ![Neena](https://avatars.discourse-cdn.com/v4/letter/n/bc79bd/32.png) [@Neena](https://gromacs.bioexcel.eu/u/Neena)\
**Post date:** [January 16, 2023, 3:25am UTC](https://gromacs.bioexcel.eu/t/pc-and-gromacs-requirements-for-remd/5438/3 "2023-01-16T03:25:14Z")

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When I attempted REMD run, I got an error - mpirun command not found. Can anyone help me verify if my system and gromacs specifications (below) are suitable for running REMD with 16 replicas?

System:  
 ![image](https://europe1.discourse-cdn.com/flex017/uploads/bioexcel1/original/2X/2/25b2a42a2cfcfacccde54f41de5295d3e24a0f69.png)

Gromacs:  
 ![image](https://europe1.discourse-cdn.com/flex017/uploads/bioexcel1/original/2X/c/c4609266711b79cba3a09559289439240e4c6e5a.png)

Thank you so much for your time and expertise,  
Neena

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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:** [January 16, 2023, 11:39am UTC](https://gromacs.bioexcel.eu/t/pc-and-gromacs-requirements-for-remd/5438/4 "2023-01-16T11:39:24Z")

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Replica exchange requires the use of an external MPI library and is very resource-intensive. If you have 16 replicas, you need **at minimum** 16 cores so that each job is assigned to one. But then, the simulations are likely to be painfully slow. Any replica exchange setup needs at least N\*M cores, where N is the number of replicas and M is the number of cores you want per replica. This usually ends up being in the hundreds of cores per job.

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**Author:** ![Neena](https://avatars.discourse-cdn.com/v4/letter/n/bc79bd/32.png) [@Neena](https://gromacs.bioexcel.eu/u/Neena)\
**Post date:** [January 20, 2023, 1:44am UTC](https://gromacs.bioexcel.eu/t/pc-and-gromacs-requirements-for-remd/5438/5 "2023-01-20T01:44:53Z")

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@jalemkul Thank you for the detailed info!