# [Pw_forum] problem about calculation with ph.x

Eyvaz Isaev eyvaz_isaev at yahoo.com
Mon Dec 29 14:13:38 CET 2008

```Dear li-ming-fan,

In order to calculate phonon dispersion curves you need to calculate real space Interatomic Force Constants matrix F(R). This can be obtained via the FFT using the dynamical matricies F(q).

In order to get F(q) set, you should use only nq1,nq2,nq3, but not iq1,iq2,iq3 which are used to calculate F(q) for a given q-point(s).

After F(q)=> F(R) transformation you have to supply a list of q-points along high symmetry directions and calculate phonon modes for these points.

Bests,
Eyvaz.

-------------------------------------------------------------------
Prof. Eyvaz Isaev,
Theoretical Physics Department, Moscow State Institute of Steel & Alloys, Russia,
Department of Physics, Chemistry, and Biology (IFM), Linkoping University, Sweden
Condensed Matter Theory Group, Uppsala University, Sweden
Eyvaz.Isaev at fysik.uu.se, isaev at ifm.liu.se, eyvaz_isaev at yahoo.com

--- On Mon, 12/29/08, lzh-ming <lzh-ming at 163.com> wrote:

> From: lzh-ming <lzh-ming at 163.com>
> Subject: [Pw_forum] problem about calculation with ph.x
> To: "Pw_forum" <pw_forum at pwscf.org>
> Date: Monday, December 29, 2008, 2:46 PM
> Hello everyone,
>   I have tried to calculate the phonon disperation of
> CdCNi3.
> I wrote in the file CdCNi3.ph.in as follow:
>
>   ldisp=.true.,
>   nq1=4, nq2=4, nq3=4,
>   iq1=2, iq2=1, iq3=1,
>
> but in the file CdCNi3.dyn0 , I got
>   4 4 4
>   1
>   0.0 0.0 0.0
>
> I changed the value of iq1,iq2,iq3 to 2,2,1, I still got
> 0.0 0.0 0.0.
> I set the value as 3 3 2, I got 0.25 0.25 0.25.
> When the value is 3 3 3, I got -0.5 -0.5 -0.5.(This is
> right.)
>
> I tried all the 10 unequivalent points of 4*4*4 grid(simple
> cube),
> I only got 3 different outputs.
>
> What's the problem? Can you help me?
>
> Thanks a lot!
>
> li-ming-fan
>
>
>
>  _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://www.democritos.it/mailman/listinfo/pw_forum

```