[Wien] Refractive index calculation using kram

[Peter Blaha]

No, you cannot do that.

You can run   x optic   on any k-mesh you like and get the momentum 
matrix elements.

But you cannot run   x joint  with an arbitrary k-mesh (I'm even 
surprised that it did not crash). joint performs an integration over the 
BZ using a tetrahedron method. So it need a tetrahedral mesh (from x kgen).


(You cannot calculate a DOS using   x tetra   either with an arbitrary 
k-mesh (except when using a simple sample method and Gauss broadening).

On 03/24/2017 09:59 AM, Yong Woo Kim wrote:
> 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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-- 

                                       P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-165300             FAX: +43-1-58801-165982
Email: blaha at theochem.tuwien.ac.at    WIEN2k: http://www.wien2k.at
WWW:   http://www.imc.tuwien.ac.at/TC_Blaha
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