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
