[Wien] imaginary dielectric function at nonzero q

[Karel Vyborny]

Hello,
in addition to what Gavin wrote, I'd remark that the implementation of 
finite q AC conductivity (which is simply related to the dielectric 
function) should not be difficult. Instead of taking (2.17) in

https://arxiv.org/pdf/cond-mat/0402523v1.pdf

you'd use Eq. 2.15 before the limit in q is taken, that's all. This is a 
standard Kubo formula result (for conductivity or epsilon). However, you 
should first sit back and think how large the q of interest will be. If it 
is much smaller than any reasonable k-mesh finesse (I mean \Delta k 
between two adjacent k-points) then you are out of luck.

Karel


--- x ---
dr. Karel Vyborny
Fyzikalni ustav AV CR, v.v.i.
Cukrovarnicka 10
Praha 6, CZ-16253
tel: +420220318459


Date: Mon, 23 May 2016 06:25:56 -0600
From: Gavin Abo <gsabo at crimson.ua.edu>
To: ben amara imen <imen.benamara5 at gmail.com>
Cc: Karel Vyborny <vybornyk at fzu.cz>
Subject: Re: [Wien] imaginary dielectric function

In the article by Ambrosch-Draxl et al. [
https://arxiv.org/pdf/cond-mat/0402523v1.pdf [arxiv.org] ], you can see on
page 26:

Furthermore, for the high energy photons the q = 0 limit is not justified
any more and thus a finite momentum transfer should be considered in 
future
work.

I think that future work for q not equal to zero was never implemented for
WIEN2k.  I believe that is because they started working on their own DFT
program called EXCITING [ https://en.wikipedia.org/wiki/EXCITING
[en.wikipedia.org] ].

If you look on the webpage for the elk branch [ 
http://elk.sourceforge.net/
[elk.sourceforge.net] ], you should see:

added dielectric function calculation for arbitrary q-vector, see
'LiF-Yambo' example (experimental)


On Sat, 21 May 2016, ben amara imen wrote:

> Hi, 
> 
> Using Wien2k , I have calculate the imaginary part of dielectric function
> (epsilon2) as function of photon energy. I have two  questions: : 
> 
> 1) How I can know at which high point symmetry , the epsilon2 is calculated
> 
> 2 ) I need to calculate , with wien2k, the imaginary part of dielectric
> function versus q  ( epsilon 2=f(q)). How can I do this ?
> 
> Thanks for your help
> 
>
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