[Pw_forum] force and stress in the Berry phase method

[Stefano Baroni]

Dear Hanghui Chen,

On Mar 30, 2009, at 10:20 PM, hanghui chen wrote:

> Dear PWSCF users,
>     In addition to my previous email, I would like to know: if I use  
> ultrasoft psedopotential, are the forces and stress correctly  
> calculated in the Berry phase method in the latest version 4.0.4?

forgive my answering your question in a rather indirect and  
pedagogical way.

this is a question that you could (actually, should) easily answer  
yourself. just repeat your calculation with (slightly) distorted  
atomic positions / cell parameters, calculate forces and stresses by  
finite differences, and compare with the results of the code. this  
way, you would do yourself and us a favor. yourself, because you would  
learn not to trust ANY code (not even the best, i.e. QE); us because  
if the code is supposed to give the right answer and id doesn't, then  
you will have helped discover a bug ...

>     Thank you very much.

Good luck!

Stefano

---
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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