[QE-users] occupation in biological molecules and band gap

[Kazume NISHIDATE]

Dear Stefano:
> For isolated molecules, smearing helps dumping the convergence
> oscillations arising from HOMO-LUMO level crossings.

I did not know it.
Thank you for the information.


Dear José Xavier,
> The band gap for Dopamine was 3.8 eV, and the other papers published
>  by them showed values between 3-5 eV. That is why I have asked

According to the paper you mentioned, they utlized the 'scissor'
correction on the band gap,

 E_g_scissor = E_g_HSE - E_g_PBE

This should be the possible reason of the discrepancies.

It is somewhat empirical way, but surprisingly, it looks me work for some
transition oxide materials, according to their paper. As far as I know,
the 'scissor' method is not well recognized in the DFT community.
#This is the first time I have ever heard of.

And there is one other point. The valence band maximum (VBM), which
corresponds to the HOMO, is located at the Y point in the BZ (see
Fig.2 of the paper).  To estimate correctly the gap from the DOS
analysis, it must include the contribution from the Y point.  The
2x2x2 mesh you mentioned is apparently insufficient.  In other wards,
you should correctly plot the band structure along typical k-points to
find the 'reasonable' band gaps.


best regards
kazume NISHIDATE
敬具 西館数芽

nisidate at iwate-u.ac.jp
kazume.nishidate at gmail.com
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