[Wien] Plasma frequency in semi-metal case and effect of band folding on optical properties

[Peter Blaha]

I thought your material has a gap, and the question was only direct or 
indirect .. ??

Of course, a supercell MUST not change the optical property. The 
momentum matrix elements should take care that there is no transition 
from Gamma - "backfolded-X" point.

Am 12.07.2013 22:25, schrieb venkatesh chandragiri:
> Dear sir,
>
> I have measured the optical properties of Fe2VAl material by creating a
> primitive like lattice which contains 16 atoms. Being a semi-metal like
> nature, Fe2VAl shows typical pseudo-gap like behaviour  in DOS spectrum.
> However, i have seen that a few orbitals are crossing each other at
> gamma point across the Fermi level. Hence, from the band structure point
> of view, it could be said that there is no gap was observed. So, i
> thought to evaluate the optical properties by implementing the intraband
> contribution in "case.injoint" file (switch 6). But, though i have found
> very few orbitals around the Fermi level, i got plasma frequency value
> about zero.  i have searched in the mailing list regarding the plasma
> frequency and found that for semiconductors and insulators, one would
> observe zero value of plasma frequency. So, why in my case, i have seen
> zero value of plasma frequency, though i have not seen any gap in my
> material band structure.
>
>
> I also need another clarification regarding the effect of "band folding"
> on the optical properties.
>
> For a similar material, Fe2VAl, i have seen band folding effects
> whenever i run the calculations by removing the symmetry of the material
> (in the super cell case). Here, in the calculations with space group, i
> have seen indirect band like crossover at gamma and X point in my band
> structure. While, for supercell case, i have seen direct band like
> overlapping of  orbitals at gamma point. As suggested by the wien2k
> mailing list, i have understood the band folding effect in the super
> cell case. But, my doubt is "whether these band folding phenomena will
> effect the optical properties or not....if yes, then what are the
> changes i could guess in the optical properties due to band folding.
>
>
> looking forward to your replies and thanks in advance.
>
> regards,
>
> venkatesh
>
>
>
>
>
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-- 
Peter Blaha
Inst.Materials Chemistry
TU Vienna
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A-1060 Vienna
Austria
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