[Wien] Refractive index calculation using kram

[Yong Woo Kim]

Dear Wien2k users,

Hello, I am currently working on obtaining transition dipole moment values
of wurtzite ZnO along a path using optic.

I have obtained some results but to check whether they are reasonable, I
have been trying to obtain the refractive index values using x kram.

It seems that if I perform x kram after obtaining the momentum matrix
elements along a certain path, (specified by xcrysden.klist for
bandstructure calculations) I get incorrect refractive index values. That
is I performed something like the following commands.

x lapw1 -band
x optic
x joint
x kram

and opticplot_lapw to see the refractive index curve. Am I not supposed to
do this and perform x optic on a regular k mesh?

I also tried the same thing without the bandstructure calculation part, i.e.

x kgen
x lapw1
x lapw2 -fermi
x optic
x joint
x kram

and the results seemed to be more reasonable but still the refractive index
values were about 0.2 lower than the known values. Is this within errors of
DFT calculation? Or is it too large and I may have done something wrong?

Also in the end I need to obtain the momentum matrix elements using the
first way, and when I do it should I use a finer k mesh before the band
calculation? That is,

x kgen
x lapw1 -band
x optic

Right now I am just using a value of 1000 used in init_lapw. Could there be
a reasonable value (or minimum value) of k points that should be used?

Thank you very much for reading the long post, and any help will be greatly
appreciated.

Yours Sincerely,
Yong Woo Kim
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