[Pw_forum] RE : positive Fermi energy

[Nicola Marzari]

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


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