[Pw_forum] positive Fermi energy

[David Grifith]

Dear Professor Giannozi and Marzari

 Many thanks for your helpful comments.

 david grifith wrote:
>
> > yet I have not understood where is selected as zero energy
> > in the Bulk graphite by QE ?  or generally where is selected
> > as zero energy in QE calculations?
>
> nothing is selected as "zero energy". One-electron energies,
> including the Fermi energy, are calculated with respect to some
> arbitrary reference energy (see the paper cited in the first of
> the following links). If you want to set your zero of the energy
> at the Fermi energy, you can do it in your preferred plotting
> program. If instead you want to know how this arbitrary reference
> level is calculatd in the code, see the notes in the last link.
>
> http://www.democritos.it/pipermail/pw_forum/2004-August/001240.html
> http://www.democritos.it/pipermail/pw_forum/2007-April/006351.html
> http://www.democritos.it/pipermail/pw_forum/2009-June/013231.html
> http://www.democritos.it/pipermail/pw_forum/2009-June/013232.html
>
> P.
> ---
> Paolo Giannozzi, Dept of Chemistry&Physics, Univ. Udine
> via delle Scienze 208, 33100 Udine, Italy
> Phone +39-0432-558216, fax +39-0432-558222
>
>
>
>
> On this thread - let me also stress that lacking an absolute
> scale of energies is an intrinsic feature of calculations
> done in periodic-boundary conditions, and not a feature or a
> defect of q-e. It's universal to any solid-state code (abinit,
> vasp, castep...). it's also very instructive to understand
> why it happens, and an extensive discussion of the issues related
> to finding the position of the vacuum level and the electrostatic
> averaging technique (Baldereschi et al Phys. Rev. Lett. 61,
> 734 (1988)) can be found in Caspar Fall's thesis
> http://library.epfl.ch/en/theses/?nr=1955 or in
> Singh-Miller et al Phys. Rev. B 80, 235407 (2009), while the
> issues related to electrostatics in periodic-boundary conditions
> are discussed in Dabo et al Phys. Rev. B 77 115139 (2008).
>
> nicola
> ?
>
> --
> ---------------------------------------------------------------------
> Prof Nicola Marzari   Department of Materials Science and Engineering
> 13-5066   MIT   77 Massachusetts Avenue   Cambridge MA 02139-4307 USA
> tel 617.4522758 fax 2586534 marzari at mit.edu http://quasiamore.mit.edu
>
>
> --
> Sincerely Yours
> David G.
> JCU
>
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