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

[José Xavier]

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
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