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

[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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