If you have a "metal", i.e. some bands cross EF, you should have a
finite (maybe small) plasma frequency (like in transparent conducting
oxides)
Am 13.07.2013 18:37, schrieb venkatesh chandragiri:
Dear sir,
*I thought your material has a gap, and the question was only direct or
indirect .. ??*
If i did the calculations using the structure stimulated from the space
group (225), it shows a negative indirect band gap in the band structure
(negative indirect band gap means, the valance band maximum falls above
the Fermi level at gamma point and conduction band minimum falls below
the Fermi level at X-point ). Then, can i expect an intra-band
contribution to my optical property. Does it give any finite value of
plasma frequency in the indirect band gap case...?
At present, i did optical calculations on the primitive cell of same
structure where i could find the band folding across the Fermi level.
Here, At gamma point, both the valance band maximum falls above the
Fermi level and conduction band minimum falls below the Fermi level,
showing a direct overlap between them due to band folding. As suggested
by your reply, the back folding of bands will not effect the system
optical properties. Then, this case is also similar to be a negative
indirect band gap like.
So, what is importance of direct, indirect and negative indirect band
gaps while calculating the optical properties....may be i should need
some examples of experimental data to understand this. Can you suggest
me some references.
Looking forward to your answers and comments.
thanks for your contributions....
regards,
venkatesh
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