# Small system - mpi error -I couldn't start em job

**URL:** <https://gromacs.bioexcel.eu/t/small-system-mpi-error-i-couldnt-start-em-job/3850>\
**Category:** User discussions\
**Created:** [March 16, 2022, 7:31pm UTC](https://gromacs.bioexcel.eu/t/small-system-mpi-error-i-couldnt-start-em-job/3850 "2022-03-16T19:31:37Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![isilayozturk](https://avatars.discourse-cdn.com/v4/letter/i/13edae/32.png) [@isilayozturk](https://gromacs.bioexcel.eu/u/isilayozturk)\
**Post date:** [March 16, 2022, 7:31pm UTC](https://gromacs.bioexcel.eu/t/small-system-mpi-error-i-couldnt-start-em-job/3850/1 "2022-03-16T19:31:37Z")

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gromacs 2022+cp2k interface

My system is small but how I can fix this mpi error. I couldn’t start em job

Command line:  
gmx\_cp2k mdrun -v -deffnm em

Compiled SIMD: AVX\_256, but for this host/run AVX\_512 might be better (see  
log).  
Reading file em.tpr, VERSION 2022 (double precision)

* * *

Program: gmx mdrun, version 2022  
Source file: src/gromacs/domdec/domdec.cpp (line 2232)  
MPI rank: 0 (out of 28)

Fatal error:  
There is no domain decomposition for 28 ranks that is compatible with the  
given box and a minimum cell size of 1.81394 nm  
Change the number of ranks or mdrun option -rdd or -dds  
Look in the log file for details on the domain decomposition

## For more information and tips for troubleshooting, please check the GROMACS website at [Common Errors — GROMACS webpage https://www.gromacs.org documentation](http://www.gromacs.org/Documentation/Errors)

* * *

## Primary job terminated normally, but 1 process returned a non-zero exit code. Per user-direction, the job has been aborted.

* * *

mpirun detected that one or more processes exited with non-zero status, thus causing  
the job to be terminated. The first process to do so was:

## Process name: [[1062,1],2] Exit code: 1

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<div class="post-metadata">

**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:** [March 16, 2022, 7:42pm UTC](https://gromacs.bioexcel.eu/t/small-system-mpi-error-i-couldnt-start-em-job/3850/2 "2022-03-16T19:42:31Z")

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Use fewer processors. Your system is too small to divide over 28 ranks.

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**Author:** ![isilayozturk](https://avatars.discourse-cdn.com/v4/letter/i/13edae/32.png) [@isilayozturk](https://gromacs.bioexcel.eu/u/isilayozturk)\
**Post date:** [March 16, 2022, 8:36pm UTC](https://gromacs.bioexcel.eu/t/small-system-mpi-error-i-couldnt-start-em-job/3850/3 "2022-03-16T20:36:18Z")

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ok thank you!