[Pw_forum] missing imaginary frequencies

[Eyvaz Isaev]

Dear Andrea,

Have you tried using more q-points? Can you send me the picture to have a look 
at?

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



----- Original Message ----
From: Andrea Salguero <ls538 at cornell.edu>
To: "pw_forum at pwscf.org" <pw_forum at pwscf.org>
Sent: Sat, January 15, 2011 1:20:18 AM
Subject: [Pw_forum] missing imaginary frequencies

Dear Pwscf community:

I have calculated the phonon frequencies of a metallic system along different 
high symmetry points in the BZ and also the phonon dispersion of it. I see two 
instabilities at z-point in the dispersion plot but I obtain no 
imaginary/negative frequencies when I calculate only for that point. I used the 
same parameters in the input files for both calculations and I followed the 
procedure from the examples directory of PWSCF(example02) for the calculation of 
the frequencies at Z point:
1) a scf calculation
2) then the calculation of the dynamical matrix at z-point (0,0,0.5), my input 
file:

&inputph
  tr2_ph=1.0d-14,
  amass(1)=183.84d0,
  amass(2)=15.9994d0,
  prefix='case',
  outdir = '',
  fildyn='case.dynZ',
/
0.0 0.0 0.5

what am I doing wrong or what am I missing?

Any help would be appreciated,

Best Regards
Andrea


********************************************************
Andrea Salguero
School of Applied and Engineering Physics
Cornell University, Ithaca NY
********************************************************
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