[gpaw-users] Problem with charged slabs

[Jaime Gómez]

    Dear gpaw-users,

    I've been employing GPAW for a few months now and  I have observed the following problem when attempting calculations with a charge. For instance:

         For Au(111) neutral slab I obtain an energy of E(Au) = -99.09 eV
         For the same Au(111) negatively charged slab (charge=-1) the energy is E(Au-) = -96.49 eV.

    so adding an electron to the slab is endothermic, +2.5 eV, however, the energy released should be close to the workfunction value, -5.1 eV.

    The cell contains 36 atoms, periodic boundary conditions in three dimensions and probably a compensating background.


    Is there any way to obtain the correct total energy for charged slabs?
    Where can I read about how the compensating charge is added?

    Thank you very much,

    Jaime Gómez-Díaz.