[Pw_forum] How/where to get DISPLACEMENT PATTERN

[Stefano Baroni]

Dear Bayleyegn Akane:

> I am graduate student at Addis Ababa Univerity-Ethiopia. Currently I  
> am working on my thesis using the Quantum-Espresso package.

welcom on board!

>   I am trying to do phonon calculation with my system relaxed. There  
> are three points that  I want to be clear about for now:
> 1. when can I say that a system is fully relaxed?

when the forces acting on atoms and the acroscopic stress are "small  
enough". How small is "small"? As small as getting it even smaller  
would not change the quantity you want to calculate (phonon  
frequencies, in you case) to within your target accuracy. What the  
target accuracy has to be, only YOU can say ...

> 2. should I do simple 'relax' prior to a 'vc-relax'?

it depends how far your volume/ cell shape is from their equilibrium  
state. all in all, it is probably safer do some experimentation by  
yourself and gain some confidence on what you are doing, than relying  
on the advice of other people ...

>
> 3. to do a 'vc-relax', what displacement pattern I better follow?

sorry: I do not quite undererstand the question ...

take care -  Stefano B

---
Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center -  
Trieste
http://www.sissa.it/~baroni / [+39] 040 3787 406 (tel) -528 (fax) /  
stefanobaroni (skype)

La morale est une logique de l'action comme la logique est une morale  
de la pensée - Jean Piaget

Please, if possible, don't  send me MS Word or PowerPoint attachments
Why? See:  http://www.gnu.org/philosophy/no-word-attachments.html






-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20090131/e717f059/attachment.html>