[Pw_forum] Phonon- Negative frequencies

[Sohail Ahmad]

Dear QE user,

While calculating phonon dispersion of ZrS2 monolayer, i am getting negative eigen values.
Though i have taken every care of convergence, q mesh and k points but all in vain.
Pls have a look at my input files mentioned below.Output file is attached.
Any suggestions are highly appreciated.

&inputph
 tr2_ph = 1.0d-15,
 ldisp = .true.,
 nq1 = 6, nq2 = 6, nq3 = 1,
 amass(1) = 91.22,
 amass(2) = 32.06,
 prefix = 'ZrS2m',
 outdir = './OUT',
fildyn = 'ZrS2m.dyn',
/

&control
  calculation = 'scf',
  restart_mode = 'from_scratch',
  prefix = 'ZrS2m',
  pseudo_dir = '/home/sohail/Espresso/espresso-5.0.1/pseudo',
  outdir = './OUT',
  verbosity = 'high',
  tprnfor = .true.,
  tstress = .true.,
  etot_conv_thr = 1.0d-5,
  forc_conv_thr = 1.0d-4,
  nstep = 500,
 /
 &system
  ibrav = 4, a = 3.75, b = 3.75, c = 15.0,
  nat = 3, ntyp = 2,
  ecutwfc = 75,
  ecutrho = 300,
  nosym = .FALSE.
  occupations = 'fixed',
 /
 &electrons
  mixing_beta = 0.7,
  conv_thr = 1.0d-15,
 /
ATOMIC_SPECIES
Zr  91.22  Zr.pbe-mt_fhi.UPF
S   32.06  S.pbe-mt_fhi.UPF
ATOMIC_POSITIONS {Angstrom}
Zr  0.000000000  0.000000000  0.000000000
S  -0.000000018  2.113679346  1.383970000
S   1.830500018  1.056839657 -1.383970000
K_POINTS AUTOMATIC
12 12 1 1 1 1
-------------- next part --------------
A non-text attachment was scrubbed...
Name: phonons.xmgr
Type: application/octet-stream
Size: 45360 bytes
Desc: not available
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20150512/f5afab21/attachment.obj>