This is an fcc lattice and shifts are breaking the symmetry and thus not
allowed.
In addition, the gap is at Gamma, so when you want epsilon at low
energies, you "need" Gamma.
PS: I've not tried other possible setups like R or B lattices or a P
supercell, but for the former symmetry will certainly be broken (you
cannot make a "cubic" k-mesh when using R or B lattices because of the
sqrt2 or 3 factors) and in the latter the computational effort will be
much larger anyway.
The optics with 200000k runs in 10 mins on a single core ....
On 09/05/2018 02:00 PM, Xavier Rocquefelte wrote:
As you Laurence, I was thinking about the effect of shifting or not the
kmesh!
Peter, do you think it will lead to a better convergence?
Cheers
Xavier
Le 03/09/2018 à 13:59, Laurence Marks a écrit :
What you are doing "should" work -- I have done similar things myself.
I have also managed to do it "not quite right" in the past as well.
The most obvious possibility is user error.
One thing I would check is shifting the k-mesh. For reasons that I do
not fully understand this can break symmetry. A good thing to check is
no shift, this may solve the problem. You may want to test using TEMPS.
You may also need to tighten the convergence. Breaking of symmetry can
be a very soft mode, and be only satisfied when one pushes to really
well converged results.
On Sun, Sep 2, 2018 at 10:33 PM, Oleg Rubel <rub...@mcmaster.ca
<mailto:rub...@mcmaster.ca>> wrote:
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 <mailto:rub...@mcmaster.ca>
Tel: +1-905-525-9140, ext. 24094
Web:
https://urldefense.proofpoint.com/v2/url?u=http-3A__olegrubel.mcmaster.ca&d=DwICAg&c=yHlS04HhBraes5BQ9ueu5zKhE7rtNXt_d012z2PA6ws&r=U_T4PL6jwANfAy4rnxTj8IUxm818jnvqKFdqWLwmqg0&m=WpMS0L_jtI19kiPXo_QJrB9iBMQX1L9TeNePUM_x2Lw&s=YKfgMS8xLL_yM_B62Rds1s_GApfimaNcCR8kQSU2LLw&e=
<https://urldefense.proofpoint.com/v2/url?u=http-3A__olegrubel.mcmaster.ca&d=DwICAg&c=yHlS04HhBraes5BQ9ueu5zKhE7rtNXt_d012z2PA6ws&r=U_T4PL6jwANfAy4rnxTj8IUxm818jnvqKFdqWLwmqg0&m=WpMS0L_jtI19kiPXo_QJrB9iBMQX1L9TeNePUM_x2Lw&s=YKfgMS8xLL_yM_B62Rds1s_GApfimaNcCR8kQSU2LLw&e=>
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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--
Professor Laurence Marks
"Research is to see what everybody else has seen, and to think what
nobody else has thought", Albert Szent-Gyorgi
www.numis.northwestern.edu <http://www.numis.northwestern.edu> ;
Corrosion in 4D: MURI4D.numis.northwestern.edu
<http://MURI4D.numis.northwestern.edu>
Partner of the CFW 100% program for gender equity,
www.cfw.org/100-percent <http://www.cfw.org/100-percent>
Co-Editor, Acta Cryst A
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