[Pw_forum] Calculating number of bands

[Lorenzo Paulatto]

Replying to message "[Pw_forum] Calculating number of bands" from  
Shaptrishi Sharma (18/12/09):
> I would like to calculate the number of bands for my system with 300  
> atoms.
> What I used to do earlier was I multiplied the total number of atoms with
> the valency and then divide the total number of bands by two in order to  
> get the valence band numbers, but now when I following this method, it is
> showing me that 'too few bands'.
>
> is there any other method also?

Dear Shaptrishi,
your method is correct, i.e. you take half the number of electrons,  
rounded up if necessary. Maybe you've just missed some electrons (do you  
have any pseudopotential with semi-core orbitals in valence?)

If you use a smearing you need more bands, the default is 20% more and at  
least 4 more. By the way, why don't you stick to the default value? It  
usually works, and even if it causes any problem you can always change it  
by hand when necessary.

best regards

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Lorenzo Paulatto
SISSA  &  DEMOCRITOS (Trieste)
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