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

[Hongyi Zhao]

On Thu, Dec 30, 2021 at 5:22 AM Kazume NISHIDATE <nisidate at iwate-u.ac.jp> wrote:
>
> 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.

To be precise, it is very difficult or almost impossible for the
selected k-points to coincide the valence band maximum (VBM) and
conduction band minimum (CBM) exactly. Therefore, the guiding
principle on energy band and dos plotting is generally taking the
enough dense k-points grid, which increases the probability that the
used k-point grid coincides with or approximates the VBM and CBM.

HZ