Fermi energy and band structure interpolation
Posted: Fri Feb 18, 2022 3:56 pm
Hi all!
I have some questions regarding QP band structure calculations, specifically how the results are reported.
It is my understanding that Yambo shifts the KS energies coming out of in this case Quantum Espresso. For example, QE output is for the first k-point has the highest occupied band at 2.4511eV, and the lowest unoccupied one at 3.223eV. It also reports a Fermi energy of 2.7509eV.
In r_setup I however see a Fermi energy of 2.84eV and at the first k-point energies of -0.391309eV and 0.380611eV (see also CBmin and CBmax) reported here:
So it roughly seems as if Yambo shifted the energies such that the Fermi energy of the DFT calculation is set to zero? Is that correct? I was under the impression that the zero should be at the VBM from previous posts?
Then, in the resulting *.qp file, also the shifted KS energies show up. With the QP shifts being "asymmetric".
However, when I interpolate a band structure with ypp, it also appears as if the GW band structure is shifted such that the middle of the gap (Fermi energy) is zero. Is this intended behavior, or is there anything that I have somehow missed?
Addition:
I was also confused by ypp's output. I am running the interpolation in batches. And I notice it reports
but does report different values for different batches. For most of them actually
What is the meaning of this and could it be possible then that different batches have different shifts?
I have some questions regarding QP band structure calculations, specifically how the results are reported.
It is my understanding that Yambo shifts the KS energies coming out of in this case Quantum Espresso. For example, QE output is for the first k-point has the highest occupied band at 2.4511eV, and the lowest unoccupied one at 3.223eV. It also reports a Fermi energy of 2.7509eV.
In r_setup I however see a Fermi energy of 2.84eV and at the first k-point energies of -0.391309eV and 0.380611eV (see also CBmin and CBmax) reported here:
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[02.05] Energies & Occupations
==============================
[X] === General ===
[X] Electronic Temperature : 0.258606E-1 300.100 [eV K]
[X] Bosonic Temperature : 0.258606E-1 300.100 [eV K]
[X] Finite Temperature mode : yes
[X] El. density : 0.29601E+24 [cm-3]
[X] Fermi Level : 2.842452 [eV]
[X] === Gaps and Widths ===
[X] Conduction Band Min : 0.341384 [eV]
[X] Valence Band Max : -0.348692 [eV]
[X] Filled Bands : 102
[X] Empty Bands : 103 300
[X] Direct Gap : 0.701256 [eV]
[X] Direct Gap localized at k-point : 9
[X] Indirect Gap : 0.690076 [eV]
[X] Indirect Gap between k-points : 8 10
[X] Last valence band width : 0.349303 [eV]
[X] 1st conduction band width : 0.309158 [eV]
Then, in the resulting *.qp file, also the shifted KS energies show up. With the QP shifts being "asymmetric".
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1 102 -0.391309 -1.192311 -0.593971
1 103 0.380611 0.451979 -3.108466
Addition:
I was also confused by ypp's output. I am running the interpolation in batches. And I notice it reports
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<---> [06.04] Fermi Levels
<---> Fermi Level (BUILT-in bands) : 2.842452 [eV]
Code: Select all
<---> [06.04] Fermi Levels
<---> Fermi Level (BUILT-in bands) : 0.000000 [eV]