Why do we need Gamma point in Band structure

[only1892]

First post,a good begin.
As far as I know,the band gap is generated from the bragg reflection at the BZ boundary.So I
think we just need the special K-point at the surface of 1BZ,and also the band gap(direct or indirect) is at the special K-point on the surface. But it seems not real in most band structure. For any structure,can we predict where is the energy gap before we do any calculation?
What I am missing in understanding the band structure?

Thanks a lot.

Wayne

 

[ZapperZ]

First post,a good begin.
As far as I know,the band gap is generated from the bragg reflection at the BZ boundary.So I
think we just need the special K-point at the surface of 1BZ,and also the band gap(direct or indirect) is at the special K-point on the surface. But it seems not real in most band structure. For any structure,can we predict where is the energy gap before we do any calculation?

To a certain point, yes we can. It totally depends on how complicated the crystal structure is, and how strongly correlated the electrons are.

The problem with calculating band structure is that you do not know a priori to what extent you have to include other interactions that may be relevant. For example, look at the tight-binding model. When do you only consider the nearest-neighbor overlap, next-nearest-neighbor overlap, next-next-nearest-neighbor, etc.. What you end up doing is making an approximation based on empirical data.

Zz.