[QE-users] Missing empty state in SCF calculation

[Paolo Giannozzi]

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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-- 
Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222