Dear Wien2k community,
I try to compute opto-elastic properties of InP (zinc-blend structure).
It is related to a change of the dielectric constant (real part) in
response to an applied strain. There are no problems with a response to
a hydrostatic strain, and results agree well with experiments. A problem
occurs with a uniaxial strain (strained along X-axis only by 0.05%).
Computed change in the dielectric constant is too large (~ an order of
magnitude).
Trying to trace back the problem, I did the following:
First, I initialize a tetragonaly-distorted zinc-blend structure
(init_lapw -b -vxc 19 -ecut -6.5 -numk 800) with the following lattice
parameters
F LATTICE,NONEQUIV.ATOMS: 2
MODE OF CALC=RELA unit=ang
11.095785 11.090240 11.090240 90.000000 90.000000 90.000000
Then I set the lattice parameters back to the cubic lattice
F LATTICE,NONEQUIV.ATOMS: 2
MODE OF CALC=RELA unit=ang
11.090240 11.090240 11.090240 90.000000 90.000000 90.000000
and rerun (x dstart). This allows me to preserve the symmetry of a
distorted structure (see the structure file below).
Next, I run SCF (run_lapw -ec 0.00001 -cc 0.0001) and optics with
20x20x20 k-mesh. The results for Re and Im parts of the dielectric
constant are here:
[oleg@feynman InP-w2k]$ head InP-w2k.epsilon
#
# Lorentzian broadening with gamma= 0.100000 [eV]
# Im(epsilon) shifted by 0.7860 [eV]
# No intraband contributions added
#
# Energy [eV] Re_eps_xx Im_eps_xx Re_eps_yy Im_eps_yy
#
0.013610 0.940850E+01 0.988634E-01 0.947674E+01 0.100908E+00
0.040820 0.940928E+01 0.100340E+00 0.947756E+01 0.102453E+00
0.068030 0.941084E+01 0.101855E+00 0.947919E+01 0.104042E+00
It seems that the symmetry is broken, which causes later problems with
opto-elastic coefficients as change of 0.07 in the second decimal point
of Re_eps for such a small strain is too much.
Once again, there are no problems when the strain tensor does not break
the zinc-blend cubic symmetry.
Any thoughts are highly appreciated.
Thank you in advance
Oleg
--
Oleg Rubel (PhD, PEng)
Department of Materials Science and Engineering
McMaster University
JHE 359, 1280 Main Street West, Hamilton, Ontario L8S 4L8, Canada
Email: rub...@mcmaster.ca
Tel: +1-905-525-9140, ext. 24094
Web: http://olegrubel.mcmaster.ca
P.S. I run WIEN2k_16.1 (Release 11/17/2016). Our main cluster is down
for maintenance, so I was not able to check with the newest version of
Wien2k.
P.P.S. Here is the cubic structure file with a distorted symmetry that I
run to get the data.
InP
F LATTICE,NONEQUIV.ATOMS: 2
MODE OF CALC=RELA unit=ang
11.090240 11.090240 11.090240 90.000000 90.000000 90.000000
ATOM -1: X=0.00000000 Y=0.00000000 Z=0.00000000
MULT= 1 ISPLIT=-2
In NPT= 781 R0=0.00001000 RMT= 2.0000 Z: 49.000
LOCAL ROT MATRIX: 0.0000000 0.0000000 1.0000000
1.0000000 0.0000000 0.0000000
0.0000000 1.0000000 0.0000000
ATOM -2: X=0.25000000 Y=0.25000000 Z=0.25000000
MULT= 1 ISPLIT=-2
P NPT= 781 R0=0.00010000 RMT= 2.0000 Z: 15.000
LOCAL ROT MATRIX: 0.0000000 0.0000000 1.0000000
1.0000000 0.0000000 0.0000000
0.0000000 1.0000000 0.0000000
8 NUMBER OF SYMMETRY OPERATIONS
1 0 0 0.00000000
0-1 0 0.00000000
0 0-1 0.00000000
1
1 0 0 0.00000000
0 0-1 0.00000000
0-1 0 0.00000000
2
-1 0 0 0.00000000
0 1 0 0.00000000
0 0-1 0.00000000
3
-1 0 0 0.00000000
0 0 1 0.00000000
0-1 0 0.00000000
4
-1 0 0 0.00000000
0 0-1 0.00000000
0 1 0 0.00000000
5
-1 0 0 0.00000000
0-1 0 0.00000000
0 0 1 0.00000000
6
1 0 0 0.00000000
0 0 1 0.00000000
0 1 0 0.00000000
7
1 0 0 0.00000000
0 1 0 0.00000000
0 0 1 0.00000000
8
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