Error in md run

GROMACS version:2021.5
GROMACS modification: Yes/No
Here post your question :
Dear users:
The error occured when I had a npt.mdp run. What I can do under this situation?
Command line:
gmx mdrun -v -deffnm npt

Compiled SIMD: AVX2_256, but for this host/run AVX_512 might be better (see
Reading file npt.tpr, VERSION 2021.5 (single precision)

NOTE: Parallelization is limited by the small number of atoms,
only starting 12 thread-MPI ranks.
You can use the -nt and/or -ntmpi option to optimize the number of threads.

Changing nstlist from 15 to 100, rlist from 2 to 2

Using 12 MPI threads
Using 2 OpenMP threads per tMPI thread

WARNING: This run will generate roughly 58315 Mb of data

starting mdrun ‘Great Red Owns Many ACres of Sand’
600000000 steps, 600000.0 ps.
step 41100, will finish Wed Nov 22 21:55:53 2023vol 0.76! imb F 212% 281%

Program: gmx mdrun, version 2021.5
Source file: src\gromacs\domdec\cellsizes.cpp (line 143)
MPI rank: 0 (out of 12)

Fatal error:
The X-size of the box (4.309420) times the triclinic skew factor (1.000000) is
smaller than the number of DD cells (4) times the smallest allowed cell size

Hi, this just indicates that you’re using too many CPUs for the size of your system. It seems though that this happens after a short while, and not at the very beginning, so my guess is that your box is shrinking over time. If your box size/shape changes, then the initial decomposition of the box into domains might not be optimal anymore.

If it’s just a small change due to density equilibration that brings the box below the minimal allowed size, then either use fewer CPUs or make the box slightly bigger.

Thank you for your suggestions!