[Pw_forum] Problem with nbnd in clusters

[Stefano de Gironcoli]

Nicola Marzari wrote:
> 6) this open up my favourite question - should B be spherical or
> cylindrical in DFT ? I.e. should we look like for occupation 1 0 0
> for the 2p levels, or 1/3 1/3 1/3 ?
>   
> 7) Last, but important - even using Gamma sampling, PWSCF finds
> for your geometry 16 symmetry operations, and thus heavily
> symmetrizes the system. That means that in 6) even 1 0 0 would
> become spherical. I.e. the symmetrization has a similar effect
> to temperature, in creating a charge density that is more symmetrical 
> /degenerate occupations than it could be.
>
> I would be *Very curious* to see what happens if you were to
> put the dimer in a very random position, so the code misses most
> of the symmetry operations, and also you specify no_sym, so no 
> symmetrization is performed.
> 			nicola\
>
>   
I agree with Nicola that this is very relevant and that symmetrization 
induces
a degeneracy that could not be there in the best "broken symmetry" solution.
This one can be achieved by 1) occupations='from_input'  2) nosym=.true.
no smearing is required then.

stefano