[QE-users] Assunto: Re: Assunto: Re: Difference in Fermi energy by increasing k-points

[Kazume NISHIDATE]

Dear Xavier:

As stated by Dr. Paolo, the figures you attached are fundamentally identical
and that indicates both of your calculations are correct.

In the figure 2 (normal_strange.pdf) the Fermi level is at the 0 eV
and there is no state between 0 eV and -5 eV.

The region is called energy gap. In this case, you can shift the Fermi
energy just down to the -5 eV and relabel it as 0 eV, so that you can
obtain the two identical DOS plots.

If there is no state bellow the calculated Fermi level, you can shit
down it until above the first occupied state (VBM or HOMO).


Happy c/lambda year!


敬具　西館
best regards

nisidate at iwate-u.ac.jp
kazume.nishidate at gmail.com
2022年1月4日 18:45 +0900、Paolo Giannozzi <p.giannozzi at gmail.com> のメール:
> The two figures are exactly the same, only the origin of the x axis is shifted.
>
> Paolo
>
> On Tue, Jan 4, 2022 at 10:29 AM José Xavier via users <users at lists.quantum-espresso.org> wrote:
> > > Dear Nishidate,
> > >
> > > Thank you for your answer.
> > >
> > > I don't know if I understood... Could you explain me better what should I do, please?
> > >
> > > I'm sending a figure of my DOS plotted using the HOMO and the EFermi as the zero, respectively, to make my doubt clearer.
> > >
> > > I learned that I should use a "large" number of k-points to converge the system. However, I only found the first figure when I used the 10x10x10 k-points in the NSCF calculation, and 2x2x2, 4x4x4 or 6x6x6 in the SCF. When I increased or decreased the k-points in the NSCF, it showed me the second figure (that is different from the reference one).
> > >
> > > I tried to use the smearing occupations. In this test, the EFermi in SCF and NSCF calculations were the same (2.74 eV), except when I used 10x10x10 k-points in the NSCF. In this case, the EFermi was 2.74 in SCF and 1.04 eV in the NSCF (it is the same value that I found previously as the HOMO in SCF calculation).
> > >
> > > My main question is: Why is this 10x10x10 a "magic number"?
> > >
> > > Best wishes.
> > > I wish you a happy new year.
> > >
> > > José Xavier
> > >
> > >
> > > >
> > > >
> > > > Em qua., 29 29e dez. 29e 2021 às 18:22, Kazume NISHIDATE
> > > > <nisidate at iwate-u.ac.jp> escreveu:
> > >
> > >
> > > >
> > > >
> > > >
> > > >
> > >
> > >
> > >
> > > Dear Xavier
> > >
> > > > When I used the k-points 4x4x4 (SCF) and 8x8x8 (NSCF), the HOMO and
> > > > EFermi were different, and using EFermi to subtract the values in the
> > >
> > > If the k-point mesh you selected covers the typical energy peaks of
> > > the valence band maximum (VBM or the HOMO in your description) depends
> > > on the shape of Brillouin zone (BZ) of your system.
> > >
> > > You should try to plot the band structure and assess the VBM and find
> > > out its k-point location. If the k-point mesh you selected does not
> > > cover the k-point, then the VBM peak will not contribute to your DOS
> > >
> > > plot.
> > >
> > >
> > >
> > >
> > >
> > > 敬具　西館
> > >
> > > best regards
> > >
> > >
> > >
> > > nisidate at iwate-u.ac.jp
> > >
> > > kazume.nishidate at gmail.com
> > > _______________________________________________
> > > Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
> > > users mailing list users at lists.quantum-espresso.org
> > > https://lists.quantum-espresso.org/mailman/listinfo/users
>
>
> --
> Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
> Univ. Udine, via delle Scienze 206, 33100 Udine, Italy
> Phone +39-0432-558216, fax +39-0432-558222
>
> _______________________________________________
> Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
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