[Wien] questions about Wien2k

[Pavel Ondračka]

> > Im using Wien2k code and I have some questions 
> > 
> > 1) Wien2k code is based on DFT which consideres only the ground
> > state but in the same time the code calculates the absorption
> > spectrum. is this spectrum has a physical sense ? it is correct ?
Quite nice summary of this problem is in the introduction to the
article by Ambrosch-Draxl (Ambrosch-Draxl, C. & Sofo, J. O. Linear
optical properties of solids within the full-potential linearized
augmented planewave method. Comput. Phys. Commun. 175, 1–14 (2006).)

> > 
> > 2) the dielectric functions  are calculated versus energy. What
> > means this energy ? is it the excitation energy ? and what means
> > the static dielectric constant
Yes, this is the photon (excitation) energy.
Static dielectric constant means the dielectric function at very low or
zero frequency.
> > 
> > Dr. K. C. Bhamu píše v Út 08. 11. 2016 v 06:08 -0800:
> I want to add one more query and want to explore part of question 2
> 
> For example,
> 1.  In a case of the optical properties for a system where we have
> a,b and c different. In such case we define xx, yy and zz in
> case.inop and get three components in the case.epcilon file. Does it
> simply mean that such materials are anisotropic along three
> directions?
Yes. For more info check the section II.B of the above mentioned
article. 
> 2. Is the average value at zero energy of a real part of dielectric
> constant is static dielectric constant? if not then how we can get
> from the output file of the case?
You can get the ! electronic part ! of the dielectric function using
the optic package. If you material is not isotropic, you will get
dielectric tensor instead. To get the electronic part of the static
dielectric tensor, just pick the first line from the epsilon file with
the near zero energy. And yes, it may make sense if you are comparing
to some experimental value (of amorphous or polysrystaline materials
with unknown grain orientation) to make an average value (by
calculating the 1/3 of the trace of the dielectric tensor).

Best regards
Pavel