[Pw_forum] band structure

[Stefano Baroni]

Dear YC Cheng,

rather than answering your question, I will give you a hint, and let  
you answer yourself. I do not know what "conventional cell" means, but  
I wil assume that for a semiconductor with an FCC Bravais lattice  
(say, with the diamond or zincblende structure) you mean the smallest  
simple cubic cell that can tile your crystal structure.

Take Silicon, for instance. The point X={2\pi\over a}(100) is the X  
point of the FCC crystal structure, but it is a reciprocal-lattice  
vector of the SC one. The bottom of the conduction band is on the  
\Delta (\Gamma-X) line, very near to the X point, whereas the top of  
the valence band is at \Gamma. the gap is therefore indirect. What  
happens if you consider the crystal as SC, rather than FCC?

Please, post your answer to this forum.

Cheers - Stefano B

On Jun 9, 2008, at 3:46 PM, 程迎春 wrote:

> Dear pwscf users,
>         I have a problem about the band structure. When I calculate  
> the band structure of an kind of semiconductor, I found an  
> inconsistent problem between using conventional cell and primitive  
> cell. The conventional cell shows the direct band gap ,while the  
> primitive one shows
> indirect band gap. My Question: what kind of band gap of this  
> semiconductor is. Any suggestion is appreciated.
>        Thank you in advance!
>
> -- 
> Y. C. Cheng
> Department of Phyics
> Nanjing University
> Nanjing 210093
> P. R. China
> Tel: 86-25-83592907
> Email: yccheng.nju at gmail.com
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---
Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center -  
Trieste
http://www.sissa.it/~baroni / [+39] 040 3787 406 (tel) -528 (fax) /  
stefanobaroni (skype)

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