effect of ISMEAR on the Fermi level during the calculation

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Gu Chenjie · #1 Post by **Gu Chenjie** » Sun Jun 10, 2012 4:39 am

Hi All,
I am trying to obtain the VBM of SiO2 from the calculation.
First, I happened to try different ISMEAR(-5/0 with different sigma), i found that the Fermi Energy/VBM in the OUTCAR is very different.
Then I fixed the ISMEAR to -5, and changed the KPOINTS (from 3X3X3 to 21X21X21), and the result show that the total energy was convergent, but the Fermi Energy still quite different under different KPOINTS condition, and no tendency to follow.
However, as mentioned in the UG of VASP, for insulator and semiconductor, ISMEAR=-5 is recommended.
SO I would like to check with those experts that whether the Fermi Energy calculated with the ISMEAR=-5 is more adoptable?
Thanks a lot.

tlchan · #2 Post by **tlchan** » Wed Jun 20, 2012 4:25 am

If the system has an energy gap, the Fermi level can be anywhere inside the gap. Depending on the algorithm to evaluate the Fermi level, the Fermi level maybe different for different calculations.

kambiz · #3 Post by **kambiz** » Mon Jun 25, 2012 3:39 am

ISMEAR equal to -5 for your bulk material is OK

Cheers