[Pw_forum] Baldereschi and MP point.

[Stefano de Gironcoli]

Dear Jiayu Dai

the Baldereschi point and MP points are efficient choice because they 
exploit the SYMMETRY properties of the system in order to sample the BZ 
on a hopefully small set of points.
In liquid and disordered materials there is no symmetry and therefore 
there is no symmetry-related k-point reduction and any regular grid of 
points should be equally efficient.
On the other hand for large systems the BZ shrinks and the refolded 
bands in the mini-BZ are almost flat which means that any single point 
in the BZ should do the work.
In this situation Gamma is convenient because  wfc (in absence of 
spin-orbit) can be chosen as real in real space which implies that wfc 
Fourier components of G and -G are related  by complex conjugation and 
you can use half the memory storage and cut by two the number of operations.

best,
  stefano

Jiayu Dai wrote:
> Dear users, 
>
> I have a question about the sample points in the Brillouin zone. We usaually use
> the MP point in our calculations, and it works well and fast in cubic crystal.
> However, for disordered materials or liquids, we usually use Gamma point only,
> such as point in CPMD. My question is how do we know the Gamma point is better
> than the Baldereschi mean value point, or on the contrary£¿Which one gives faster
> convergence?
>
> Thanks a lot.
>
> Jiayu
>
>
>
>
> ------------------------------
> -------------------------------------------
> Jiayu Dai
> Department of Physics
> National University of Defense Technology, 
> Changsha, 410073, P R China
> -----------------------------------------
>   
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>
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