[Pw_forum] phonon calculations in a spercell of 100 atoms

[Lorenzo Paulatto]

On Mon, 13 Feb 2012 16:36:55 +0100, Elie M <elie.moujaes at hotmail.co.uk>  
wrote:
> Dear all,
> I have two questions:
> (1) I am running phonon calculations on a system of 100 atoms  and only  
> at the Gamma point!  It is really taking a lot of time. It is running in  
> the parallel computing mode with a total of 16 processors on 2 nodes and  
> still is going slow. Is there a way to speed up things? and is there a  
> way to do the whole phonon dispersion in lesser time?

Do not use a supercell? Seriously, phonon calculations are expensive, with  
many atoms they are extremely expensive. If you only need the phonons at  
the gamma point, it may be faster to get them by finite displacement,  
doing 3*nat pw.x ground state calculations.

> (2) If only the phonon  frequencies at the Gamma point were calculated ,  
> I was wondering what kind of information about the system can one get?
> Thanks

If the supercell is large enough, all the information you need.

bests


-- 
Lorenzo Paulatto IdR @ IMPMC/CNRS & Université Paris 6
phone: +33 (0)1 44275 084 / skype: paulatz
www:   http://www-int.impmc.upmc.fr/~paulatto/
mail:  23-24/4é16 Boîte courrier 115, 4 place Jussieu 75252 Paris Cédex 05