[Pw_forum] Fermi energy in 'scf' and 'nscf'(XQ Wang)

[wangxinquan]

>Dear Wang,
  Dear Prasenjit,
>
>In principle both the scf & nscf should give exactly the same value of Fermi
>energy if your calculations are converged w.r.t. the k-point sampling
>(since evaluation of Fermi energy involves numerical integration in
>k-space).The fact that that the two procedures give different energies
>suggest that the k-point mesh is not converged. Since these are numerical
>integrations, the more the no of k-points the more accurate is the value of
>the integral. Therefore for Guoying's case, the value of Fermi energy
>obtained from scf is more accurate than that from nscf as suggested by
>Hande.
>
>If the difference in Fermi energy is quite large, what I would suggest is to
>increase the no. of k-points in the nscf cal. & redo it.

As I'm a newbie in this field, the basic concept of quantum mechanics and 
condensed matter physics(DFT, the Bloch theory and plane wave) are rather
abstract for me, following contents may have some misunderstanding of your suggestions.