[Pw_forum] Acoustic sum rule in 2D surfaces

[Lorenzo Paulatto]

On 25/05/17 07:19, Charlie Ruffman wrote:
> On a related topic, we were interested in how the choice of supercell 
> size might influence the vibrational modes we calculate. For instance, 
> looking at a the smallest repeatable unit of our system naturally 
> yields fewer vibrational modes than simulating a cell of 2 or 3 times 
> the size. We were wondering whether allowing the extra freedom 
> associated with a larger cell might actually map worse 
> onto experimental results?

Hi,
unless there is something that breaks symmetry (like a defect, 
substitution, long-range spin order, charge density wave...) the 
supercell will give exactly the same result as the unit cell. It is even 
possible to map (aka unfold) the supercell phonon dispersion to the unit 
cell one, although I cannot recall the name of any specific tool that 
does it at this moment.

regards

-- 
Dr. Lorenzo Paulatto
IdR @ IMPMC -- CNRS & Université Paris 6
phone: +33 (0)1 442 79822 / skype: paulatz
www:   http://www-int.impmc.upmc.fr/~paulatto/
mail:  23-24/423 Boîte courrier 115, 4 place Jussieu 75252 Paris Cédex 05

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20170525/7d41f87b/attachment.html>