[gpaw-users] parallel settings

[Ask Hjorth Larsen]

Hello Zhiyao

You have 4 k-points which probably reduce to 2 in the irreducible BZ.

That means you have 48 cores sharing two k-points, so each group of 24
will band parallelize amongst themselves as chosen by the defaults.
Since PW mode does not have domain decompositions, the only allowed
amount of band parallelization is 24 (wherefore 4 is an illegal
number).  That's quite a lot and I would expect it to run a bit
slowly.

As Marcin says, FD mode might well be more efficient.

Best regards
Ask

2015-03-12 17:22 GMT+01:00 Zhiyao Duan <gump_813 at hotmail.com>:
> Hello everyone,
>
> I  am just starting to use gpaw and have a problem in setting parallel
> parameters.
> my system contains 96 atoms 840 valence electrons and 720 orbitals, 2 kpts
> in IBZ and
> grid points is  28*180*336. I was trying to
> run the calculation with 48 cores using the following script:
>
> import numpy as np
> from ase import Atoms
> from gpaw import GPAW, PW, FermiDirac, MethfesselPaxton
> from ase.optimize import FIRE,BFGS
>
> np.seterr(under="ignore")
>
> model=read('au_tio2.vasp',format='vasp')
>
> calc = GPAW(xc='PBE',
>             mode='pw',
>             kpts=(4, 1, 1),
>             random=True,
>             eigensolver='rmm-diis',
>             txt='au_tio2_relax.txt')
>
> model.set_calculator(calc)
> opt = BFGS(model)
> opt.run(0.05)
>
> write('final_relax.vasp',model, format='vasp',direct=True)
>
> the job can run normally but much slower than vasp with similar setups.
> I thought the slowness is due to parallelization, so I add
> parallel={'band':4} to divide bands to 4 groups. This time the job failed
> with
> error:
>
> File "/usr/local/gpaw/lib/python/gpaw/mpi/__init__.py", line 939, in
> autofinalize
>     raise RuntimeError('All the CPUs must be used')
> RuntimeError: All the CPUs must be used
>
> can anybody help me figuring out why this happens?
>
> Another question is how to compare the speed of gpaw and vasp?
> As I mentioned above, on my system vasp seems much faster, maybe this is due
> to number of valence electrons included in the calculation? In my case, Ti
> atom has 12 valence electrons in gpaw comparing to 4 in vasp. Or the better
> performance of vasp is
> due to some other factors like parallelization?
>
> Thank you guys!
>
> Zhiyao
>
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