Differrent Fermi levels with different k-paths

[Lian]

Dear VASP users.

I wanted to perform bandstructure calculations. Therefore, I first did a self-consistent charge density calculation to obtain the CHGCAR file. This calculation gave a Fermi level of -3.2570 eV for pristine graphene (rectangular unit cell optimized geometrically).

Afterwards, I did several bandstructure calculations using the calculated CHGCAR file for different paths in the Brillouin zone. In fact, I wasn't able to do the calculation for the full path Gamma-X-M-Y-Gamma-M, and thus splitted into 5 small paths (5 different calculations), which are the following:

path 1
0.0000000000000000 0.0000000000000000 0.0000000000000000 ## G
0.5000000000000000 0.0000000000000000 0.0000000000000000 ## X

path 2
0.5000000000000000 0.0000000000000000 0.0000000000000000 ## X
0.5000000000000000 0.5000000000000000 0.0000000000000000 ## M

path 3
0.5000000000000000 0.5000000000000000 0.0000000000000000 ## M
0.0000000000000000 0.5000000000000000 0.0000000000000000 ## Y

path 4
0.0000000000000000 0.5000000000000000 0.0000000000000000 ## Y
0.0000000000000000 0.0000000000000000 0.0000000000000000 ## G

path 5
0.0000000000000000 0.0000000000000000 0.0000000000000000 ## G
0.5000000000000000 0.5000000000000000 0.0000000000000000 ## M

However, I found out that the Fermi levels are different. From path 1 to 5, the Fermi levels are -3.7473, -4.3789, -3.4765, -3.2571, -3.6720 eV.
As you should have noticed, these Fermi levels are different from the one obtained during the self-consistent calculation, except from path 4 (Y-Gamma).
Interestingly, the path Y-Gamma is the one in which we observe the Dirac point (not at K since my graphene unit cell is rectangular instead of hexagonal)

I do not understand why it is like that. May I trust the bandstructures I obtained ?
I point out that the INCAR file was the same for every paths; only the KPOINTS file was changed.

Thanks for your help.

Best regards.
Yan

[admin]

in ab initio codes, the Fermi level is the KS energy of the highest occupied state.