Disclaimer: Assume the questioner is a novice in DFT and condensed matter physics in general.

How reliable are DFT based estimates of the fermi energy? Do different flavours of DFT affect the accuracy of these estimates? If yes, how?

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    $\begingroup$ I made a small edit, I dont think there is a need to get different answers for different flavors of DFT. I think that will come naturally as people talk about improvements or problems. $\endgroup$ Oct 14 '20 at 13:59
  • $\begingroup$ @TristanMaxson alright, makes sense. $\endgroup$ Oct 14 '20 at 14:00

Usually, it is assumed that the Fermi energy is the energy of the highest occupied electronic state. It is well defined for metals with partially filled bands. For semiconductors and dielectrics, however, there may be a discrepancy between different software packages, since the Fermi energy can correspond to the center of the bandgap at 0 K in the case of an undoped semiconductor or it can be at the top of the valence band. The former convention pins the Fermi energy to the energy of a state which has the occupation probability of 0.5 even at T>0 K.

  • $\begingroup$ But in metals one has to use fractional occupations. Is it even well defined which orbitals are occupied and which are not? $\endgroup$ Oct 15 '20 at 23:06

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