[Pw_forum] Problem with nbnd in clusters

[Stefano de Gironcoli]

Stefano de Gironcoli wrote:
> 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.
>
>   
indeed with this input I get

!    total energy              =  -121.76929092 Ry
     Harris-Foulkes estimate   =  -121.76929090 Ry
     estimated scf accuracy    <        1.9E-09 Ry
 
which I think is the correct result...
stefano






> stefano
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