Fermi level problem of GW-band

[sunxl]

Dear all:

When I use the GW method to calculate the band structure, according to the tutorial, I first calculate the DFT band structure. However, when I look at the output file, I find that the DFT band structure results show that the Fermi level is located at -1.9 eV, which would pass through my band structure, making my structure a metal, while it is actually a semiconductor with a 1.6 eV bandgap, as shown in the output. Why is this happening?

I appreciate any guidance and tutorial on that!

[05.05] 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 : 0.10853E+24 [cm-3]
[X] Fermi Level : -1.939240 [eV]

[X] === Gaps and Widths ===
[X] Conduction Band Min : 0.820113 [eV]
[X] Valence Band Max : -0.818621 [eV]
[X] Filled Bands : 15
[X] Empty Bands : 16 200
[X] Direct Gap : 1.780568 [eV]
[X] Direct Gap localized at k : 18
[X] Indirect Gap : 1.638734 [eV]
[X] Indirect Gap between kpts : 25 55
[X] Last valence band width : 0.318761 [eV]
[X] 1st conduction band width : 1.303551 [eV]

Best，
sunxl

[Daniele Varsano]

Dear Sunxl,

please sign your post with your name and affiliation, this is a rule of the forum. You can do this once for all by filling the signature in the user profile.
What you observe, it is not a problem.
Yambo by convention shift the energies and set the zero energy at the top of the valence band. You can convince yourself looking at the energies reported in the report file.
The reported Fermi level is not calculated after GW correction, this is the Fermi level of the Kohn-Sham band structure as calculated by QE (indicated with X), and it is reported just for reference. When the whole electronic structure is recalculated after QP correction (eg. in BSE calculations) it is indicated with X+QP.
So, in your case, you have an indirect semiconductor with the gap indicated. Being a semiconductor, the Fermi energy will be at the top of the valence band or in the middle of the gap, depending on the convention.

Best,

Daniele