Deriving accurate work functions from thin-slab calculations

Quantum-size effects have been shown to influence significantly the determi nation of work functions from thin-slab calculations. We show here that a t echnique based on macroscopic averages can be used to reduce such effects a nd determine more precisely the work functions of metals from ab initio thi n-film calculations. The technique combines the mean electrostatic potentia l step across the slab surface with the Fermi energy of a bulk crystal. The method is applied to Al(100) slabs containing 1-14 atomic layers.