[QE-users] Missing empty state in SCF calculation

[Paolo Giannozzi]

On 01/09/2023 18:17, Lorenzo Sponza wrote:

> Dear Paolo, thanks for the answer.
> I made a check running the same two calculations using the CG
> diagonalization scheme instead of Davidson. The issue persists. May I
> send you the input files ?

not a good idea, because I don't think it is a bug and don't have a 
solution at hand. You may open an issue on gitlab, though.

Paolo

> Best
> 
> 
> Le 2023-09-01 16:49, Paolo Giannozzi a écrit :
>> Iterative diagonalization may occasionally miss one or a few states if
>> the starting manifold does not contain enough components of the
>> missing states. As long as you do not miss any states in the occupied
>> manifold, not a big deal for the ground-state calculation (but not for
>> the band gap, of course)
>>
>> Paolo
>>
>> On 9/1/23 16:41, Lorenzo Sponza wrote:
>>>
>>> You don't often get email from lorenzo.sponza at onera.fr. Learn why this
>>> is important <https://aka.ms/LearnAboutSenderIdentification>
>>>
>>>
>>> Dear all,
>>>
>>> I encounter an issue I did not expect and I would like to know why it
>>> happens and how I am suppose to handle it. I'm running an SCF
>>> calculation of a gapped system (occupations = 'fixed'). If I include a
>>> large number of empty bands, these are the energies in Gamma:
>>>
>>> -4.8200-4.3169-0.9586-0.5478-0.5196-0.4977-0.0537 0.0095 with
>>> occupations 1.0000 1.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000
>>>
>>> Instead, if I include only one empty band the result is
>>>
>>> -4.8200-4.3169-0.5477 with occupations 1.0000 1.0000 0.0000
>>>
>>> It's like in if the latter case I was missing the state at -0.9586 eV.
>>> How it happens ?
>>>
>>> I'm rising this issue because I'm checking the gapwidth of a series of
>>> similar systems. I actually thought that it was safe to run simple SCF
>>> calculations with 1 empty state, but I realise that results are
>>> possibly wrong. Shall I mandatorily rely on NSCF calculations or I'm
>>> making a mistake somewhere ?
>>>
>>> Best regards
>>>
>>> -- Dr. Lorenzo Sponza
>>> Chargé de Recherche au CNRS
>>> Laboratoire d'étude de microstructures (LEM), CNRS-ONERA
>>> 29 Avenue de la division Leclerc, 92322 Châtillon
>>> Tel: +33146734464
>>>
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> 
> -- 
> Dr. Lorenzo Sponza
> Chargé de Recherche au CNRS
> Laboratoire d'étude de microstructures (LEM), CNRS-ONERA
> 29 Avenue de la division Leclerc, 92322 Châtillon
> Tel: +33146734464
> _______________________________________________
> The Quantum ESPRESSO community stands by the Ukrainian
> people and expresses its concerns about the devastating
> effects that the Russian military offensive has on their
> country and on the free and peaceful scientific, cultural,
> and economic cooperation amongst peoples
> _______________________________________________
> Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
> users mailing list users at lists.quantum-espresso.org
> https://lists.quantum-espresso.org/mailman/listinfo/users

-- 
Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 206, 33100 Udine Italy, +39-0432-558216