[QE-users] Negative frequencies in Phonon dispersion of PdS2 bilayers

[Sohail Ahmad]

 Dear QE users
I am trying to calculate the phonon dispersion curves of PdS2 BILAYERS
but it always give negative frequencies of the order of ~ -8 cm-1.
Please have a look at my input file and feel free to edit it to make
it more meaningful
---------------------------------------------------------------------------------------------------------------
&control
  calculation = 'scf',
  restart_mode = 'from_scratch',
  pseudo_dir='~/pseudo_directory',
  outdir='./OUT',
  prefix='PtS2bs0',
/
&system
  ibrav = 4, a = 3.52, b = 3.52, c = 20.0, cosAB = -0.5, cosAC = 0.0,
cosBC = 0.0,
  nat = 6, ntyp = 2,
  ecutwfc = 75,
  ecutrho = 300,
  nbnd = 40,
  occupations = 'smearing', smearing = 'gaussian', degauss = 0.001,
  /
&electrons
  mixing_beta = 0.3,
  conv_thr = 1.0d-9,
  electron_maxstep = 900,
/
ATOMIC_SPECIES
Pt  195.08  Pt.pbe-mt_fhi.UPF
S  32.06  S.pbe-mt_fhi.UPF
ATOMIC_POSITIONS  angstrom
Pt  0.00000000  0.00000000  0.00000000
S  1.80374872  1.02665089  1.24494264
S  -1.80374872 -1.02665089 -1.24494264
Pt  0.00000000  0.00000000  6.70000000
S  1.80374872  1.02665089  7.94494264
S  -1.80374872 -1.02665089  5.45505736
K_POINTS AUTOMATIC
16  16  4  0  0  0
-----------------------------------------------------------------------------
#phonon of unstrained structure
&inputph
 prefix = 'PtS2bs0',
 tr2_ph = 1.0d-16,
 ldisp = .true.,
 search_sym = .false.,
 nq1 = 2, nq2 = 2, nq3 = 1,
 amass(1) = 195.08,
 amass(2) = 32.06,
 outdir = './OUT',
 fildyn = 'PtS2bs0.dyn',
/
----------------------------------------------------------------------------------
&input
fildyn = 'PtS2bs0.dyn',
zasr = 'simple',
flfrc = 'PtS2bs0.fc',
/
-------------------------------------------------------------------------------
&input
asr = 'simple',
amass(1) = 195.08,
amass(2) = 32.06,
flfrc = 'PtS2bs0fc',
flfrq = 'PtS2bs0.freq',
/
        240
        0.0000000000    0.0000000000    0.0000000000    1.0
        0.0057471264    0.0000000000    0.0000000000    1.0
        0.0114942529    0.0000000000    0.0000000000    1.0
        0.0172413793    0.0000000000    0.0000000000    1.0
        0.0229885057    0.0000000000    0.0000000000    1.0
        0.0287356322    0.0000000000    0.0000000000    1.0
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