[Pw_forum] missing imaginary frequencies

[Andrea Salguero]

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


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