[CP2K:4890] Re: PBE0 MULTIPLICITY 1 calculation

[carlo antonio pignedoli]

Dear Marcella, thanks a lot for your reply
no it's not really metallic otherwise I would give up.

Yes I think that for this system PBE0 is quite meaningful
for similar ones it considerably opens the gap giving results more
in agreement fo G0W0 and here I am quite curious to
see what it will do to the magnetic solutions.

I forgot that smearing breaks the MULTIPLICITY constraint, I will try
without smearing

Ciao, thanks a lot

Carlo


On Tue, Jan 14, 2014 at 4:50 PM, marci <marc... at pci.uzh.ch> wrote:

> Dear Carlo,
>
> since you used the smearing of the occupation numbers, the multiplicity is
> not constrained.
> The occupation of the eigenstates is assigned according to their energy,
> irrespective of alpha and beta.
> The Fermi energy is then determined consistently for the full electronic
> system, and it is -0.14381945698278 a.u. in your case.
>
> If this is really meaningful for your system, I do not know.
> Is this really a metallic system, as it apparently results from this
> calculation?
> Is PBE0 appropriate for a metallic system?
>
> ciao
> Marcella
>
> Il giorno martedì 14 gennaio 2014 12:08:05 UTC+1, c.pignedoli ha scritto:
>
>> Dear all,
>>  I am doing a PBE0 calculation for a periodic quasi 1D system (a graphene
>> nanoribbon)
>>
>> I did restart the calculation from a converged antiferromagnetic PBE
>> calculation
>>
>> The PBE0 calculation terminated with a unequal number of alpha and beta
>> orbitals thus violating (I guess) the MULTIPLICITY 1 of the input and of
>> the restart.
>> (
>> 355 alpha and 349 beta while it should be  352 alpha and 352 beta
>> this can be seen checking   the added mos
>> declared at the end of the file: should have been 100 and 100 instead it
>> is 97 102
>> and form the file with occupation numbers of the states (which I do not
>> include)
>> )
>>
>> I enclose the input file and the output, what is scaring is a sudden jump
>> of the energy at
>> the beginning of the SCF (from -980 to -1200 at step 24 of the scf) that
>> could be related to problems with the coulomb cutoff.
>>
>>
>>
>> Does anybody have suggestions about what could be wrong?
>> Could it be that the cell size is too small for this particular system
>> (however it is big enough
>> to have a fair PBE description)?
>> (Basically I have 12 unit cells of a zig-zag graphene nanoribbon with at
>> least 20A of vacuum in the non periodic directions, the PBE UKS
>> calculationn produces the correct edge states but of course these states
>> are nearly metallic and have, in PBE a small gap)
>>
>> Kind regards
>>
>>
>> Carlo
>>
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