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

[José Xavier]

Dear Nishidate,Thank you for your answer.
If I understood correctly, you are telling me to plot the DOS using the EFermi to subtract the energy (first column of the DOS file), and set it as the zero. Is it?

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 DOS file to set it equal to the zero changed the peaks, with the last peak of the Valence band ending close to -5 eV. On the other hand, when I used the HOMO value (1.04 eV) to "set the zero", this peak ended in the zero point. The same occur when I use the k-points 6x6x6 (SCF) and 12x12x12 (NSCF).
However, when I use the k-points 4x4x4 or 6x6x6 (SCF) and 10x10x10 (NSCF), the EFermi is equal to HOMO (1.04 eV) and the plot of the DOS is "correct", with the last peak of Valence band ending in the zero point.
I don't understand why only these two values of kpoints in SCF and 10x10x10 in NSCF  gave me "correct" peaks, at the same time, why all the other combinations I've tried gave me a "strange" arrangement in the peaks. 
Best wishes.And thank you again for answer my question
José Xavier
Enviado do Yahoo Mail no Android 
 
  Em qua., 29 29e dez. 29e 2021 às 2:13, Kazume NISHIDATE<nisidate at iwate-u.ac.jp> escreveu:   
Dear Xavier,

> performed a calculation using 6x6x6 k-point in SCF (fixed
> occupations) and 10x10x10 in NSCF (tetrahedra occupations). The E
> fermi was equal to the HOMO value (1.04 eV). However, when I increase
> (e.g. 8x8x8 and 12x12x12,

It is normal that the Fermi level changes for the calculation to
calculation with different set of k-points or cutoff energies.
Because the energy standard (energy zero) can not be defined solely in
the DFT calculation.

> respectively) or decrease (e.g. 4x4x4 and 8x8x8) the number of
> k-points in each calculation, the E fermi (6.03 eV) and HOMO (1.04
> eV) are quite different.

You should try to plot the DOS figures with shifting the energy
scale. The easiest way to do this is to set the E fermi equal to 0.

E(4x4x4) = E(4x4x4) - 1.04
E(6x6x6) = E(6x6x6) - 6.03

The resultant DOS figures of the two will be identical.
敬具　西館
best regards

nisidate at iwate-u.ac.jpkazume.nishidate@gmail.com2021年12月29日 5:17 +0900、José Xavier via users <users at lists.quantum-espresso.org> のメール:

Dear QE users,

I performed a calculation using 6x6x6 k-point in SCF (fixed occupations) and 10x10x10 in NSCF (tetrahedra occupations). The E fermi was equal to the HOMO value (1.04 eV). However, when I increase (e.g. 8x8x8 and 12x12x12, respectively) or decrease (e.g. 4x4x4 and 8x8x8) the number of k-points in each calculation, the E fermi (6.03 eV) and HOMO (1.04 eV) are quite different.

Could someone explain to me why is this happening?


Sincerely,
José Xavier
Department of Biophysics and Pharmacology
Federal University of Rio Grande do Norte
Natal, Brazil
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