Dear all
Just to add a bit of personal experience that might be useful to
others. Let's admit that many k-points are necessary to provide a good
description of the electronic properties of a given system, this is
generally true in the case of metal systems. This fact might not
extend to the potential, and very tiny differences might be found in
final structures optimized by using a coarser sampling of the
Brillouin zone. In the huge cell shared by Hongyi Zhao, I would start
a geometry optimization from a gamma-only simulation and then I would
check if forces on ions were low enough with a 2x2x1 mesh. If this was
not the case, I would fully optimize the system with the new mesh and
go a step ahead, and so on up to a decent convergence of the
potential. Then I would perform nscf calculations with increasing
numbers of k points followed by, e.g., dos.x post processing runs, to
check the convergence of the density of states (be careful, because
AFAIK nscf runs overwrite the results of the scf run). Of course, all
of this depends on the specific purpose of the calculation, but in my
past experience with molecules on metal surfaces this strategy saves a
lot of time and resources.
HTH
Giuseppe
Quoting Sebastian Hütter <sebastian.huet...@ovgu.de>:
Hi,
This may be a stupid question, but...
Estimated static dynamical RAM per process > 3.32 GB
Estimated max dynamical RAM per process > 10.52 GB
Estimated total dynamical RAM > 462.96 GB
... is this not expected behavior? I'm not super experienced, so I
just assumed it was.
Your numbers pretty much match what I see in terms of "RAM per Cell
volume" in metals with non-symmetric unit cells using PAW pseudos,
if not less. Random example: 126 atoms, 63 k-points, ~1000 bands,
250³ dense grid FFT gives ~10GB per rank, for a total of 680GB with
64 ranks. I actually plan node requests for our cluster based
entirely on memory required, probably wasting CPU time along the way
(4N*16C in the example above).
Reasonable ke and charge cutoffs seem to blow up the memory
requirements a lot. Of course multiplied by the number of bands...
Best,
Sebastian
--
M.Sc. Sebastian Hütter
Otto-von-Guericke University Magdeburg
Institute of Materials and Joining Technology
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GIUSEPPE MATTIOLI
CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
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E-mail: <giuseppe.matti...@ism.cnr.it>
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