[Pw_forum] cutoff convergence of sapphire for elastic properties

Jörg Buchwald joerg.buchwald at iom-leipzig.de
Mon May 7 15:22:07 CEST 2012

i tested a relaxed sapphire structure  using a 10x10x10 k point set with
a cutoff energy up to 250 Ry. Even at this Energy, a change of +/- 5 Ry
in the cutoff lead to stresses of the order of 1 kbar.
I used for Al and O pbe-n-van US pseudo potentials from the pseudo
folder of quantum espresso. But also pbe-sp-van for Al and rrkjus for
oxygen led to the same problem. 
I don't have a clue how high the cutoff must be, but 250 Ry seems to be
far too high. Is that a problem of the pseudopotentials or does
it have something to do with physical structure of sapphire?
Thx for any hints,
Jörg Buchwald

Leibniz-Institut fuer Oberflaechenmodifizierung e.V.

Permoserstrasse 15
04318 Leipzig

Phone: +49 341 / 235-3367
Web: http://www.uni-leipzig.de/~agmayr

More information about the users mailing list