[QE-users] scf convergency depends on the number of mpi processes !!!

[Mahmoud Payami Shabestari]

Hi All,



I am experiencing that the success in scf cycle depends on the number of 
processes used in mpirun. That is, for example, for a given scf input when I 
use "mpirun -np 2 pw.x < input.in",

it gives the converged result in a reasonable number of iteration; but, on 
the other hand, if I instead use "mpirun -np 8 pw.x < input.in", the system 
does not converge numerically.

First I thought it is somehow a problem of numerical error accumulation. So, 
I used in compilation of QE the FFTW3 as prescribed in the manual. And even 
used "-lfftw3l" (long-double) to cure this problem, but some other numerical 
problems happened in vc-relax job.



I would appreciate if anybody helps to understand the roots of this 
dependency and how to control it.



Bests,

Mahmoud Payami

NSTRI, AEOI, Tehran, Iran



Email: mpayami at aeoi.org.ir
Phone: +98 (0)21 82066504
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