Dear all,
also, as mentioned several times in this mailing list:
1) extensive tests for the pseudopotentials have been done, and
are reported here:
https://www.materialscloud.org/discover/sssp/table/efficiency
2) same for kpoints and convergence tolerance
https://www.materialscloud.org/work/tools/qeinputgenerator
These two tools should not remove the need to test and understand, but
would be a solid starting point to understand if you need a higher
cutoff, more k-points, etc...
nicola
On 15/01/2020 10:25, Matic wrote:
Hi Matthew,
I've often heard it said that 1meV/atom is a good criterion for
convergence tests to set ecutwfc, ecutrho and K-point sampling. I
wonder if that makes
sense in if the structure has very light and heavy atoms. One I'm
working on now contains Ca, Si, O and H. Since each H contributes
only one electron, should
it count equally in the tally of 104 atoms? Should the criterion be a
certain energy/total electron? Energy/valence electron (defined in
the pseudo)?
Convergence of ecutwfc/ecutrho is a property of the pseudpotential used,
so you should converge ecutwfc/ecutrho for the each new atom type
(pseudopotential) in your system and then used the maximum value
obtained for all calculations. A hint for appropriate values is
typically listed in the pseudopotential file. The easiest way to do this
is just to make a small box containing the atom and increase ecutwfc
(using lets say ecutrho=8*ecutwfc_max) until the energy stays within
approx ~1 mRy. Once you obtain the converged ecutwfc then you can
decrease ecutrho to a more appropriate value.
Here is a hands-on presentation from a workshop where this is described:
http://indico.ictp.it/event/7921/session/320/contribution/1261/material/0/
Best Regards,
Matic
--
----------------------------------------------------------------------
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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