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
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