[QE-users] Band gaps from SCF vs NSCF calculations

[Nicola Marzari]

Several possibilities - simplest is that the SCF calculation is done 
with a coarse mesh, and the top of the valence and/or the bottom of the 
conduction are not located at points on this mesh.

[BTW, they do not need to be located, either, along the path you chose 
to plot the band strcture]

Try with a mterials that has a direct band gap at Gamma, using unshifted 
sampling meshes (e.g. 6 6 6 0 0 0)

nicola

On 28/08/2019 19:46, MARIA CATERINA CEVALLOS BRENES wrote:
> Dear QE developers and users:
> 
> I was computing the band gaps from scf calculations as the difference 
> between HOMO and LUMO energies. Nonetheless, when I perform the bands' 
> calculation and plot the band structure I notice this band gap is a lot 
> less than the one I computed initially (with scf).
> 
> Am I doing something wrong? Or what am I exactly computing when I take 
> the HOMO LUMO difference in the scf-calculation.
> 
> Thank you very much!
> 
> Caterina Cevallos,
> 
> University of Costa Rica.
> 
> 
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-- 
----------------------------------------------------------------------
Prof Nicola Marzari, Chair of Theory and Simulation of Materials, EPFL
Director, National Centre for Competence in Research NCCR MARVEL, EPFL
http://theossrv1.epfl.ch/Main/Contact http://nccr-marvel.ch/en/project