[QE-users] Either NEGATIVE FREQUENCY or CONVERGENCE problem in PHONON

[Sohail Ahmad]

Dear QE experts
I am trying to calculate the phonon of NiCrSi using QE 6.5.

Either i get negative frequency or it does not converge
I tried with different values of convergence criteria, q mesh, alpha_mix in ph.in and k mesh in scf.in
tr2_ph = 1.0d-14, or
tr2_ph = 1.0d-12, or
tr2_ph = 1.0d-16,

nq1 = 4, nq2 = 4, nq3 = 4, or 
nq1 = 3, nq2 =3, nq3 = 3, or
  nq1 = 2, nq2 = 2, nq3 =2,

alpha_mix(1) = 0.7, or
  alpha_mix(1) = 0.3,

K_POINTS12 12 12 or16 16 16 
What could be the possible reason of getting negative frequency if the structure is considered as stable ? Appreciate if someone point out the possible mistakes
Best Wishes
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#phonon of NiCrSi structure
&inputph
prefix = 'NiCrSi',
tr2_ph = 1.0d-14,
ldisp = .true.,
nq1 = 4, nq2 = 4, nq3 = 4,
amass(1) = 51.99,
amass(2) = 28.08,
amass(3) = 58.69,
  alpha_mix(1) = 0.7,
outdir = './OUT',
fildyn = 'NiCrSi.dyn',
/
&control
  calculation = 'scf',
  restart_mode = 'from_scratch',
  prefix = 'NiCrSi',
  pseudo_dir = '/home/sohail/pseudo',
  outdir = './OUT',
/
&system
ibrav = 2, a = 5.4559000675, b = 5.4559000675, c = 5.4559000675,
cosAB = 0.0, cosBC = 0.0, cosAC = 0.0,
  nat = 3, ntyp = 3,
  ecutwfc = 75,
  ecutrho = 300,
  nbnd = 25,
  occupations = 'smearing', smearing = 'gaussian', degauss = 0.001,
/
&electrons
  mixing_beta = 0.3,
  conv_thr = 1.0d-9,
/
ATOMIC_SPECIES
Cr  51.99  Cr.pbe-sp-van.UPF
Si  28.08  Si.pbe-n-van.UPF
Ni  58.69  Ni.pbe-nd-rrkjus.UPF
ATOMIC_POSITIONS  {alat}
Cr  0.00000000  0.00000000  0.00000000
Si  0.50000000  0.50000000  0.50000000
Ni  0.25000000  0.25000000  0.25000000
K_POINTS AUTOMATIC
12 12 12 0 0 0
--------------------------------------------------------------------- 

Sohail Ahmad

Department of Physics

Faculty of Science, P. O. Box - 9004

King Khalid University

Abha, Saudi Arabia


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