[Pw_forum] positive Fermi energy

[david grifith]

   Dear Cyrille and Users

  Thanks for your answer. However, I don't want to calculate the energy of
vacuum; Really I want to draw the DOS and PDOS of the BULK graphite
correctly. I don't know that I should use the +7.8 eV as the Fermi energy in
the DOS diagram either set it to zero and rescale the other energies or
something else ?



  You should know that within DFT calculations the zero of energy of a
> periodic system is NOT the vacuum.
>



    where is the zero of energy here ? and in which way the QE chooses it ?



 Also, can one compare this Fermi energy with the Fermi energy of another
material, or  is such comparison reliable ?



>  If you want to get the energy of vacuum you can simulate for example a
> surface with the "supercell" method  ie including empty space between slabs.
> You will get the vacuum energy (and therefore also the work function) by
> plotting the potential far away from you slabs in the "empty" region.
>
> cyrille
>
> Dear All
>
> I get positive Fermi energy (+7.8 eV) for bulk graphite by Quantum
> Espresso.
> Positive energy is meaningless for me here. Would you please say me that in
> whcih way QE selects the zero energy?
> As I know the vacuum should be considered as zero energy.  I appreciate you
> in advance to solve the problem.
>
> --
> Sincerely Yours
> David G.
> JCU
>
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