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
David,
You should know that within DFT calculations the zero of energy of a periodic
system is NOT the vacuum. If you want to get the energy of vacuum you can
simulate for example a surface with the "supercell" method ie including empty
space between slabs. You will get the vacuum energy
