[Pw_forum] Fourier interpolation

[HaoPan]

Dear Baroni,

The kpoint grid I chose is 60*60*60.     
    nk1=60, nk2=60, nk3=60,

I think that is fine enough. Because the q point grid is just 6*6*6. 
For metal, the frequencies of the gamma point are  alway not zero (some small negative value) . 
Some may cause the frequencies around the gamma point negative. But even all q points I got are 
positive, there exit negative frequencies after the matdyn.x calculation. I don't know why.

Sincerely,
Pan Hao
Tulane University


the kpoint grid you are using may be too coarse
dynamical matrices in metals are indeed smooth functions of k, unless you have Kohn anomalies
SB

On Jul 28, 2010, at 5:33 PM, HaoPan wrote:

> Hi, everyone,
> 
> On each q point I got, the phone frequencies are positive. But after the Fourier interpolation process, There
> exist negative frequencies. I check the some special q points using ph.x, there are no negative frequencies. I
> know the dynamical matrices for metal are not smooth function of q, but how do I fix it to get the right
> dispersion curves? Thanks a lot.
> 
> Sincerely,
> Pan Hao
> Tulane University _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://www.democritos.it/mailman/listinfo/pw_forum
 		 	   		  
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20100730/b79ac25b/attachment.html>