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

[Kazume NISHIDATE]

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.jp
kazume.nishidate at gmail.com
2021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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