Fully agree with this! If I can add, using the Baldereschi point (or, to
make it simple, 1/4 1/4/ 1/4 in crystal coordinates), and nosym=.true.
allows you to do a calculation with one k-point that is almost as
accurate as using a 2x2x2 shifted monkhorst pack mesh (i.e. 2 2 2 1 1
1), at a cost that is only twice as large as a Gamma only calculation.
If a metal, use 0.03 Ry of smearing (either m-p or m-v), and indeed you
are good to go for a fast but quite accurate relaxation.
nicola
On 27/05/2020 13:39, Giuseppe Mattioli wrote:
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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--
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Prof Nicola Marzari, Chair of Theory and Simulation of Materials, EPFL
Director, National Centre for Competence in Research NCCR MARVEL, EPFL
http://theossrv1.epfl.ch/Main/Contact http://nccr-marvel.ch/en/project
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