[QE-users] Missing empty state in SCF calculation

[Lorenzo Sponza]

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 ?
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:
>> 
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>> 
>> 
>> 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