[Pw_forum] Fourier interpolation

[Eyvaz Isaev]

Dear Hao,


> The kpoint grid I chose is 60*60*60.     

I suppose you vast time with such kind incredibly large k-mesh.

Try increasing nq's for phonon calculations (ph.in). Play around 
cutoff energy and the threshold parameter for phonons.

What is the accuracy of your q2r.x (FFT) run?

Bests,
Eyvaz.
-------------------------------------------------------------------
Prof. Eyvaz Isaev, 
Department of Physics, Chemistry, and Biology (IFM), Linkoping University, 
Sweden 

Theoretical Physics Department, Moscow State Institute of Steel & Alloys, 
Russia, 

isaev at ifm.liu.se, eyvaz_isaev at yahoo.com




________________________________
From: HaoPan <adehaopan at hotmail.com>
To: pw_forum at pwscf.org
Sent: Thu, July 29, 2010 9:49:32 PM
Subject: [Pw_forum] Fourier interpolation

 
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 _______________________________________________
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