[Pw_forum] Phonon anomaly in GaSb

[Gokhan GOKOGLU]

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 )
 **************************************************************************