[Wien] Unusual behaviour observed in the momentum matrix elements calculation

[VIVEK PANDEY]

Dear Wien2K community,
             I am currently using the latest version of the WIEN2k
package (*Version:
WIEN2k_23.2*). At certain point of my work, I am in need of momentum matrix
elements ( *<nk|vx|mk>* ), where *nk* and *m*k are the indices of Bloch
states. Here, *n* & *m* denotes the band-indices and *k* stands for the
particular *k*-point of the Brillouin zone. I found from here (
https://triqs.github.io/dft_tools/latest/faqs/faqs.html#x-optic-does-not-write-a-case-pmat-file)
that one can obtain the momentum matrix elements using the *x optic* module.
For this, I need to modify the *case.inop* file as mentioned in the above
link. The momentum matrix elements will be contained in the *case.pmat*
 file.

I would like to highlight that *TaAs doesn't have inversion symmetry but
possess considerable strength of SOC*. Also, here I am performing non-spin
polarized calculations. Regarding this, the userguide reads: "*In cases of
non-spinpolarized spin-orbit calculations WITHOUT inversion symmetry one
must do some tricks and “mimick” a spinpolarized calculation*". In the
present case, to generate the TaAs.pmat file, I have followed the
following steps.

   - *Took a scf-converged folder (with SOC)*
   - *x kgen -fbz   (generated 8 points, just for checking purpose)*
   - *run_lapw -so -s lapw1 -e lcore*
   - *cp TaAs.vsp TaAs.vspup*
   - *cp TaAs.vsp TaAs.vspdn*
   - *cp TaAs.vectorso TaAs.vectorsoup*
   - *cp TaAs.energyso TaAs.energysoup*
   - *x lapw2 -fermi -so -up*
   - *x optic -so -up*


My *TaAs.inop *file look-like:







*500 1       number of k-points, first k-point0.572903715 1.057994381 9999
Emin, Emax for matrix elements, NBvalMAX2             number of choices
(columns in *outmat): 2: hex or tetrag. case1             Re xx3
  Re zzON           ON/OFF   writes MME to unit 41*

This produces the pmat file as (some of the initial lines of the
*TaAs.pmatup* file) :
       1      79     102
  0.000000000000  0.000000000000  0.000000000000         1
 (7.532302704505345E-002,8.167223407989921E-013)
 (-2.452818645937255E-002,-5.617391534568084E-012)
 (-2.736308582684184E-009,7.097544424488960E-006)
 (-3.998615698872405E-002,2.777014533732855E-002)
 (1.302109113438884E-002,8.527865972100164E-002)
 (-1.026926403886681E-010,1.200070342578796E-010)
 (-1.791111955708441E-002,5.236942743794264E-002)
 (-3.899495437248428E-002,2.316018225850822E-002)
 (3.763225250509643E-002,-7.797121255922022E-003)
 (7.310146318006450E-002,-1.059709078143053E-002)
 (-3.652737960637320E-002,-7.161172405686120E-002)
 (1.068047033704979E-002,-2.846154200524592E-002)
 (7.610044364078097E-002,6.031752549762000E-002)
 (-3.292267660532026E-003,7.254003661389334E-002)
 (-3.375310650422014E-010,-6.926246219766473E-009)
 (-4.035365458096263E-002,3.022214437391330E-002)
 (6.674399181287456E-002,-4.736686924751896E-002)
 (7.125860558467264E-010,-4.391983650614438E-009)
 (-1.849323572944582E-003,9.216247127675071E-005)
 (9.836142143746737E-004,1.454250471303621E-003)

Now, I have performed the same steps on another computer. Here, I want to
specially highlight that *I* *Took the same scf-converged folder (with SOC)
*and *performed the same steps as mentioned above (with the same TaAs.inop
file and the TaAs.klist file). Only I have done these calculations on a
different PC. *To my surprise, now I am getting different values in the
*TaAs.pmatup* file, which is shown below.
       1      79     102
  0.000000000000  0.000000000000  0.000000000000         1
 (-1.214159087495217E-002,-5.600747865703096E-014)
 (8.045331706420837E-004,-5.000950391645387E-012)
 (1.836020562752319E-010,7.097544236721407E-006)
 (8.866257188263187E-002,5.929833225268443E-003)
 (-5.875000758651897E-003,8.949005485342118E-002)
 (-9.539115301314537E-011,1.978797799446000E-010)
 (4.155953914982438E-002,-3.846832311555534E-002)
 (3.909488619796690E-002,5.101528227938528E-002)
 (1.510824184241179E-003,-3.533078749450909E-002)
 (5.739778691473076E-002,-4.492185969678203E-002)
 (4.437764328880048E-002,4.918477575252587E-002)
 (1.739430397746836E-003,3.387537549328652E-002)
 (-4.779075848660323E-002,6.299577197014268E-002)
 (6.329168974258584E-002,3.712633656957084E-002)
 (3.923592277339212E-010,1.128917508969145E-009)
 (3.378630332312889E-002,-6.765602685801606E-002)
 (-6.810286018561787E-002,-4.414831302200305E-002)
 (3.059394194239015E-010,5.748344979517646E-010)
 (-1.368362945645098E-003,-9.656884465217919E-004)
 (9.797714419467955E-004,-1.155838456028902E-003)

To me, this is not making any sense at all. Thus, there is a high chance
that I am missing something or doing something wrong.

Kindly help me with this. Also, please correct me if I am misinterpreting
something at some point.

*Thanks and Regards*

*Yours Sincerely*
Vivek Pandey
Research Scholar
Indian Institute of Technology, Mandi
Himachal Pradesh, India
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