[Pw_forum] cutoff convergence of sapphire for elastic properties

[Jörg Buchwald]

that was also done.
JB

Am Mon, 7 May 2012 09:41:35 -0400
schrieb Iyad AL-QASIR <iyad.ne at gmail.com>:

> Hello,
> Try first to relax the atomic positions, then relax the structure.
> 
> Thanks
> 
> 
> On Mon, May 7, 2012 at 9:22 AM, Jörg Buchwald
> <joerg.buchwald at iom-leipzig.de
> > wrote:
> 
> > Hi,
> > 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
> >
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> 
> 
> 



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04318 Leipzig
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