[Pw_forum] Error "Not diagonalizing because representation xx is not done" in "image" parallelization by ph.x

[Coiby Xu]

Dear Quantum Espresso Developers and Users,


I'm running a phonon calculation parallelizing over the representations/q
vectors. For my cluster, there are 24 cores per node. I want to use as many
nodes as possible to speed up the calculation.

I set the number of parallelizations to be the number of nodes,

> mpirun -np NUMBER_OF_NODESx24  ph.x -nimage NUMBER_OF_NODES
>


If I only use 4 nodes (4 images), 8 nodes ( 8 images), the calculation will
be finished successfully. However, more than 8 nodes, say 16 or 32 nodes,
are used, each time running the calculation, such error will be given,

> Not diagonalizing because representation  xx is not done
>

Btw, I want to reduce I/O overhead by discarding `wf_collect` option, but
the following way doesn't work (the number of processors and pools for scf
calculation is the same to that in phonon calculation)

mpirun -np NUMBER_OF_NODESx24  pw.x
>

ph.x complains,

> Error in routine phq_readin (1):pw.x run with a different number of
> processors.
> Use wf_collect=.true.
>

The beginning output of pw.x,

>     Parallel version (MPI), running on    96 processors
>      R & G space division:  proc/nbgrp/npool/nimage =      96
>      Waiting for input...
>      Reading input from standard input
>

and the beginning output of ph.x,

>  Parallel version (MPI), running on    96 processors
>      path-images division:  nimage    =       4
>      R & G space division:  proc/nbgrp/npool/nimage =      24
>

Do I miss something? I know it's inefficient to let pw.x use so many
processors, but it seems to be one requirement to let ph.x and pw.x have
the same number of processors.

Thank you!

-- 
*Best regards,*
*Coiby*
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