[Pw_forum] Dielectric constant calculations for InAs
Zhiping Xu
xuzp at tsinghua.edu.cn
Tue Sep 8 11:48:30 CEST 2015
Dear all:
I am using pw.x and ph.x to calculate the dielectric constant of InAs, and here are some problems with the calculations.
(1) After structural relaxation using vc-relax, the stress is now zero (confirmed using scf calculations for the final structure).
convergence has been achieved in 10 iterations
Forces acting on atoms (Ry/au):
atom 1 type 1 force = 0.00000000 0.00000000 0.00000000
atom 2 type 2 force = 0.00000000 0.00000000 0.00000000
Total force = 0.000000 Total SCF correction = 0.000000
entering subroutine stress ...
total stress (Ry/bohr**3) (kbar) P= 0.00
0.00000001 -0.00000000 -0.00000000 0.00 -0.00 -0.00
-0.00000000 0.00000001 0.00000000 -0.00 0.00 0.00
-0.00000000 0.00000000 0.00000001 -0.00 0.00 0.00
However, the following phonon calculation predicts not only negative phonon frequency at q = 0, but also very strange dielectric constant.
Dielectric constant in cartesian axis
( -230.720680077 -0.000000000 0.000000000 )
( -0.000000000 -230.720680077 0.000000000 )
( 0.000000000 0.000000000 -230.720680077 )
Effective charges (d Force / dE) in cartesian axis
atom 1 In
Ex ( 9.55076 0.00000 0.00000 )
Ey ( 0.00000 9.55076 0.00000 )
Ez ( 0.00000 0.00000 9.55076 )
atom 2 As
Ex ( -9.43886 0.00000 0.00000 )
Ey ( -0.00000 -9.43886 -0.00000 )
Ez ( 0.00000 0.00000 -9.43886 )
Diagonalizing the dynamical matrix
q = ( 0.000000000 0.000000000 0.000000000 )
**************************************************************************
freq ( 1) = -6.064621 [THz] = -202.293974 [cm-1]
freq ( 2) = -6.064621 [THz] = -202.293974 [cm-1]
freq ( 3) = -6.064621 [THz] = -202.293974 [cm-1]
freq ( 4) = 0.164141 [THz] = 5.475159 [cm-1]
freq ( 5) = 0.164141 [THz] = 5.475159 [cm-1]
freq ( 6) = 0.164141 [THz] = 5.475159 [cm-1]
**************************************************************************
The input files are attached below for your reference.
(2) One more question, the vc-relax calculation converges at zero stress, which was calculated using the cut-off set for initial cell parameters, so one has to redo the calculations using the new cell parameters following the suggestion at http://www.quantum-espresso.org/faq/self-consistency/#6.11 <http://www.quantum-espresso.org/faq/self-consistency/#6.11>. Is there any better (more automatic) way to obtain a final relaxed cell/atom structures?
Could any one help me on these two questions?
Thank you,
Zhiping
input files:
—scf.in—
&control
calculation = 'scf',
restart_mode = 'from_scratch',
pseudo_dir = '/home/xuzp/bin/lib/upf_files',
outdir = '.',
prefix = 'InAs',
tstress = .true.
tprnfor = .true.
wf_collect = .true.
/
&system
ibrav = 2,
celldm(1) = 11.69675,
nat = 2,
ntyp = 2,
ecutwfc = 90,
/
&electrons
diagonalization = 'cg'
conv_thr = 1.0d-10
/
ATOMIC_SPECIES
In 111.818 In.pbe-dn-rrkjus_psl.0.2.2.UPF
As 74.920 As.pbe-n-rrkjus_psl.0.2.UPF
ATOMIC_POSITIONS crystal
In 0.00 0.00 0.00
As 0.25 0.25 0.25
K_POINTS automatic
9 9 9 0 0 0
—ph.in—
phonons of InAs
&inputph
tr2_ph = 1.0d-16,
niter_ph = 100,
prefix = 'InAs',
epsil = .true.
amass(1) = 111.818,
amass(2) = 74.920,
outdir = '.',
fildyn = 'InAs.matdyn',
/
0.0 0.0 0.0
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