[Wien] optics broken symmetry
Laurence Marks
L-marks at northwestern.edu
Mon Sep 3 13:59:53 CEST 2018
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 <rubelo at 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 at 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: rubelo at 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=yHlS04HhBraes5BQ9ueu5zKhE7rtNX
> t_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 ; Corrosion in 4D: MURI4D.numis.northwestern.edu
Partner of the CFW 100% program for gender equity, www.cfw.org/100-percent
Co-Editor, Acta Cryst A
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