[gpaw-users] Error from transformers.py when restarting a calculation

[Peder Olesen]

Hi all,

I'm attempting to calculate some electron-phonon coupling matrix elements,
and for that purpose I need to reuse a calculator. However, when I produce
the file calcUC.gpw using the script:

from ase import *
> from gpaw import *
> a = 3.5691245496
> b = a/2.
>
> bulkUC = Atoms('C2',positions=([0,0,0],[b/2,b/2,b/2]),
> cell=([0,b,b],[b,0,b],[b,b,0]),pbc=False)
> bulkUC.set_pbc(True)
>
> calcUC = GPAW(kpts=(20,20,20), xc='PBE', h=0.2, txt='calcUC.out',
> nbands=-1)
> bulkUC.set_calculator(calcUC)
> e=bulkUC.get_potential_energy()
> calcUC.write('calcUC.gpw')
>

...and subsequently attempt to load it using any script with the lines

from gpaw import *
calcUC = GPAW('calcUC.gpw', txt='calcUC.out')

...I recieve the following error whenever the the above lines are in a
script using n>23 cores

Traceback (most recent call last):
>   File "mat_elem.py", line 2, in ?
>     calcUC = GPAW('calcUC.gpw', txt='calcUC.out')
>   File "/home/camp/s082073/gpaw/gpaw/paw.py", line 116, in __init__
>     self.initialize()
>   File "/home/camp/s082073/gpaw/gpaw/paw.py", line 571, in initialize
>     magmom_a, par.hund)
>   File "/home/camp/s082073/gpaw/gpaw/density.py", line 74, in initialize
>     allocate=False)
>   File "/home/camp/s082073/gpaw/gpaw/transformers.py", line 143, in
> Transformer
>     t = _Transformer(gdin, gdout, nn, dtype, allocate)
>   File "/home/camp/s082073/gpaw/gpaw/transformers.py", line 48, in __init__
>     assert ((gdin.n_c[0] + 2 * nn - 1) * (gdin.n_c[1] + 2 * nn - 1) <=
> AssertionError
>

If I do a dry-run=n with n=23 i get

Traceback (most recent call last):
>   File "mat_elem.py", line 2, in ?
>     calcUC = GPAW('calcUC.gpw', txt='calcUC.out')
>   File "/home/camp/s082073/gpaw/gpaw/paw.py", line 116, in __init__
>     self.initialize()
>   File "/home/camp/s082073/gpaw/gpaw/paw.py", line 518, in initialize
>     domain_comm, parsize)
>   File "/home/camp/s082073/gpaw/gpaw/grid_descriptor.py", line 124, in
> __init__
>     raise ValueError('Grid too small!')
> ValueError: Grid too small!
>

whereas n<23 gives no problems at all. I would like to use n>23 cores for
some subsequent operations. Obviously the problem has something to do with
parallelization, but does anyone know in greater detail what the particular
reason the above errors might be, and what I should do to avoid them?

Thanks in advance,
Peder J. Olesen
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