[QE-users] dielectric constant calculation

[Jay Wai]

Dear users,

I am trying to calculate dielectric constants of graphene.
I first relaxed the structure using the following pw.x input:

&CONTROL
   calculation      = 'relax'
   tstress          = .true.
   tprnfor          = .true.
   prefix           = 'noiso'
   forc_conv_thr    = 1.d-4
/
&SYSTEM
   ibrav            = 0
   ecutwfc          = 64
   ecutrho          = 576
   ntyp             = 1
   nat              = 8
   nosym          = .true.
/
&ELECTRONS
  conv_thr=1.d-12
/

ATOMIC_SPECIES
C 12.0 C.pbe-n-rrkjus.UPF

K_POINTS automatic
12 12 1  0 0 0

CELL_PARAMETERS angstrom
2.45951214674781 4.26000000000000 0.00000000000000
-2.45951214674781 4.26000000000000 0.00000000000000
0.00000000000000 0.00000000000000 30.00000000000000

ATOMIC_POSITIONS angstrom
C        0.000000000   1.420000000   15.000000000
C        0.000000000   2.840000000   15.000000000
C       -1.229756073   3.550000000   15.000000000
C       -1.229756073   4.970000000   15.000000000
C        1.229756073   3.550000000   15.000000000
C        1.229756073   4.970000000   15.000000000
C        0.000000000   5.680000000   15.000000000
C        0.000000000   7.100000000   15.000000000

And then, I calculated the dielectric constants using the following ph.x
input:

phonons of gr
 &inputph
  tr2_ph=1.0d-14,
  prefix='noiso',
  epsil=.true.,
  ldisp=.true.,
  nq1=3,
  nq2=3,
  nq3=1,
  amass(1)=12,
  fildyn='noiso.dynG',
 /

The result of calculation does not seem to be physically reasonable (very
large negative value):
          Dielectric constant in cartesian axis
          (   -6123.274083490       0.000008052      -0.000001008 )
          (       0.000008023   -6123.274129001      -0.000006809 )
          (      -0.000000922      -0.000006871       1.074380904 )

Could you give me a clue on which part of my input files might cause this?

Best,
Jay
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