[Pw_forum] Phonon anomaly in GaSb

[Eyvaz Isaev]

Dear Gokhan,

A sketch of the dynamical matrix you provided is not enough to draw a conclusion. It would be better if you post your input file. 
If you are sure your input file is correct, check another PsPs.

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 Fri, 6/20/08, Gokhan GOKOGLU <ggokoglu at hacettepe.edu.tr> wrote:

> From: Gokhan GOKOGLU <ggokoglu at hacettepe.edu.tr>
> Subject: [Pw_forum] Phonon anomaly in GaSb
> To: pw_forum at pwscf.org
> Date: Friday, June 20, 2008, 11:58 AM
> Dear PWSCF users,
> I  tried to calculate phonon dipersion of zincblende GaSb,
> but I found large
> negative modes at Gamma-point. The same system was studied
> by Giannozzi et al.
> in a previous study (PRB 43, 7231 (1991)) using LDA
> functionals and the obtained
> dispersion was quite nice without  any  anomalous
> vibrational property. I used
> GGA (PW91) vanderbilt US PP. I also checked the kinetic
> energy cut-off (70 Ry)
> and k-mesh (16x16x16) for convergence. I didn't find
> any phonon anomaly in AlSb
> with similar geometry. I give the dynamical matrix below. I
> would be very
> grateful, if someone could give an idea. Thank you very
> much..
> 
> Gokhan Gokoglu
> Dept. Physics
> Bilkent University, Ankara, Turkey     
> 
> 
> Diagonalizing the dynamical matrix
> 
>      q = (    0.000000000   0.000000000   0.000000000 )
> 
> 
> **************************************************************************
>      omega( 1) =      -9.779567 [THz] =    -326.213411
> [cm-1]
>  ( -0.646207  0.000000  0.460941  0.000000 -0.354330 
> 0.000000 )
>  (  0.367516  0.000000 -0.262150  0.000000  0.201517 
> 0.000000 )
>      omega( 2) =      -9.779567 [THz] =    -326.213411
> [cm-1]
>  (  0.504782  0.000000  0.707669  0.000000  0.000000 
> 0.000000 )
>  ( -0.287083  0.000000 -0.402471  0.000000  0.000000 
> 0.000000 )
>      omega( 3) =      -9.779567 [THz] =    -326.213411
> [cm-1]
>  ( -0.288464  0.000000  0.205762  0.000000  0.793757 
> 0.000000 )
>  (  0.164057  0.000000 -0.117023  0.000000 -0.451432 
> 0.000000 )
>      omega( 4) =      -0.606056 [THz] =     -20.215980
> [cm-1]
>  (  0.172018  0.000000  0.676699  0.000000  0.095247 
> 0.000000 )
>  (  0.173197  0.000000  0.681338  0.000000  0.095900 
> 0.000000 )
>      omega( 5) =      -0.606056 [THz] =     -20.215980
> [cm-1]
>  ( -0.434105  0.000000  0.184061  0.000000 -0.523697 
> 0.000000 )
>  ( -0.437081  0.000000  0.185323  0.000000 -0.527287 
> 0.000000 )
>      omega( 6) =      -0.606056 [THz] =     -20.215980
> [cm-1]
>  (  0.527775  0.000000 -0.069163  0.000000 -0.461794 
> 0.000000 )
>  (  0.531394  0.000000 -0.069637  0.000000 -0.464960 
> 0.000000 )
> 
> **************************************************************************
> 
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