[QE-users] Fwd: under estimate the bandgap in Quantum espresso

[Giovanni Cantele]

Dear
Prasad, there are not sufficient data to understand what's happening.

1) DFT systematically underestimates band gaps, to what extent depends on
the material. If this is the case there is nothing to do unless moving to
other approximations that at least partially solve this problem
(DFT+U,hybrid functionals,GW,....)
2) do the references you mention concern theoretical estimations within DFT
or experimental data? While when comparing with experiments you
might experient the limit of the previous point, whereas if you find other
calculations, within the same level of approximation, you should find at
least
similar (if not equal) results
3) in the case you have reference calculations to compare with and there is
no agreement, check your input geometry and unit cell (to understand if they
are wrong) as well as the convergence parameters (Brillouin zone sampling,
wave function cutoff, charge density cutoff if it applies, ....)

Giovanni

-- 

Giovanni Cantele, PhD
CNR-SPIN
c/o Dipartimento di Fisica
Universita' di Napoli "Federico II"
Complesso Universitario M. S. Angelo - Ed. 6
Via Cintia, I-80126, Napoli, Italy
e-mail: giovanni.cantele at spin.cnr.it <giovanni.cantele at spin.cnr.it>
Phone: +39 081 676910
Skype contact: giocan74

ResearcherID: http://www.researcherid.com/rid/A-1951-2009
Web page: https://sites.google.com/view/giovanni-cantele/home


Il giorno ven 16 feb 2024 alle ore 10:40 PRASAD SANKALPA WANNINAYAKA <
2019s17502 at stu.cmb.ac.lk> ha scritto:

> Dear QE users,
> I am studying the electronic properties of FeTiO3 using QE when
> calculating the band structure using 'bands.x' calculation. I obtained the
> bandgap as 0.01eV but according to references that value is 2.54 eV. i need
> to know why this is happening.
>
> Thank you
> Best regards
> Prasad Sankalpa
> Physics Undergraduate
>
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