[Wien] Concerns on the obtained values of momentum matrix elements

[Peter Blaha]

The change of sign might simply be a phase change. Since wave functions 
can change by a phase (exp(i phi)) and are still the same wave 
functions,  also the corresponding momentum matrix elements might show this.

About the abrupt change of the matrix elements I can only speculate: 
There are 2 bands crossing (either in VB or CB) and the wave function 
changes character .... ???

Did you check your band structure ?

Am 29.11.2016 um 17:16 schrieb Yong Woo Kim:
> Dear Wien2k users,
>
> Hello, I am running wien version 14.2 on linux compiled with gfortran.
>
> Right now I am trying to calculate the momentum matrix elements of Al2O3 sapphire.
> I have managed to get some results but some part of the results worry me that I may have done it wrong.
> I am particularly interested in the matrix elements between the highest valence and the lowest conduction band.
>
> The following is part of the results that I have obtained along the Gamma-A direction that I want to obtain the results for.
>
> 36	37	-0.475170000000000	2.31369000000000e-11	0.464830760000000
> 36	37	-0.475054000000000	2.33653000000000e-11	0.464900790000000
> 36	37	-0.474937000000000	2.35933000000000e-11	0.464971500000000
> 36	37	0.474819000000000	-2.38216000000000e-11	0.465042880000000
> 36	37	0.474699000000000	-2.40493000000000e-11	0.465114930000000
> 36	37	0.474579000000000	-2.42775000000000e-11	0.465187660000000
> 36	37	-0.474457000000000	2.45054000000000e-11	0.465261060000000
> 36	37	0.474334000000000	-2.47330000000000e-11	0.465335140000000
> 36	37	-0.474210000000000	2.49604000000000e-11	0.465409880000000
> 36	37	0.474085000000000	-2.51880000000000e-11	0.465485300000000
> 36	37	0.473959000000000	-2.54153000000000e-11	0.465561390000000
> 36	37	0.473832000000000	-2.56427000000000e-11	0.465638150000000
> 36	37	-0.473704000000000	2.58700000000000e-11	0.465715590000000
> 36	37	-7.66604000000000e-13	-8.84059000000000e-18	0.465756180000000
> 36	37	1.32939000000000e-11	-3.78270000000000e-19	0.465793770000000
> 36	37	-6.20312000000000e-13	-1.29951000000000e-17	0.465831680000000
> 36	37	-6.78245000000000e-12	-2.77438000000000e-17	0.465869910000000
> 36	37	1.13307000000000e-11	-2.48713000000000e-17	0.465908460000000
> 36	37	-2.17293000000000e-12	5.12272000000000e-17	0.465947330000000
> 36	37	7.86763000000000e-12	-1.91488000000000e-17	0.465986520000000
>
> 36 and 37 are the band index for my valence and conduction band. Each row refers to a k point along the G-A path and I have 501 rows in total.
>
> I also eliminated the x,y components and leaved only the z component plus the energy difference.
>
> One minor concern is that the signs of the values change and this doesn't seem to be right.
>
> Another concern is that as can be seen from the real part of z above, the value suddenly drops to less than 1e-10 order.
>
> Although not shown here, at the same k point, the real part of the x component showed the opposite behaviour,
>
> increasing from less that 1e-10 to about 0.4. This abrupt change doesn't seem to be right either.
>
> The procedure went like this.
>
> run_lapw
>
> create case.klist_band
>
> x lapw2 -fermi
>
> x lapw1 -band
>
> x optic
>
> I have tried this for different k mesh by using x kgen and run_lapw repeatedly from 1000 to 15000 and the results only had minor differences.
>
> Any help would be really appreciated.
>
> Thank you very much in advance.
>
> Yong Woo Kim
>
>
>
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-- 
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
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Email: blaha at theochem.tuwien.ac.at    WIEN2k: http://www.wien2k.at
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