[Pw_forum] maybe a bug in the QE 4.0.4 (Stefano Baroni)

[Stefano Baroni]

I am confused: no electric field, no Berry phase - what I suggested  
you to try is whether the stress calculated from finite differences  
and from the Hellmann-Feynman theorem give the same result (no Berry  
phase in either case). I am confident they do. SB

On Apr 2, 2009, at 7:12 AM, hanghui chen wrote:

> Yes. At vanish electric field, even with USPP the stress is the same  
> as the normal calculation (without using Berry Phase method).
> Hope this helps.
>
> Is your calculated stress OK with USPP at vaishing electric field?
> SB
>
> On Apr 1, 2009, at 4:48 PM, hanghui chen wrote:
>
> > Dear PWscf developers and in particular Professor Baroni,
> >       Thank you very much for your instructions.
> >       I did the test to check the forces and stress in the Berry
> > phase method with the ultrasoft pseudopotential. The forces are
> > correct but the stress is around 50% smaller. I am not sure whether
> > it is due to the ultrasoft pseudopotential or not.
> >       I would greatly appreciate it if the developers of QE could
> > reexamine the calculation of stress in the Berry phase method with
> > the ultrasoft pseudopotential.
> >       Best wishes.
> >
> > Hanghui Chen
> > Department of Physics,
> > Yale University
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---
Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center -  
Trieste
http://stefano.baroni.me [+39] 040 3787 406 (tel) -528 (fax) /  
stefanobaroni (skype)

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