Quantum size effects in metal films: Energies and charge densities of Pb(111) grown on Cu(111) - art. no. 235405

Energies and electron densities of free-standing Pb(111) slabs consisting o f 1 to 15 layers have been determined by means of ab initio total energy ca lculations, using periodic slab geometries and gradient-corrected density f unctional theory. Two sets of calculations were carried out, one with fixed slab geometries and another one where interlayer spacings were fully relax ed. We find quantum size effects (QSE's) for the total energies in agreemen t with experiments by Toennies et al. [Europhys. Lett. 10, 341 (1989)], who monitored the epitaxial growth of thin Pb films on a Cu(111) substrate. QS E's are also observed for the surface electron density of thin lead films w hich manifest themselves as different "apparent step heights" of the indivi dual layers in high resolution helium atom scattering [Surf. Sci. 384, L858 (1997)]. For this second QSE, we find that the interplane relaxation but a lso the in-plane strain within the Pb layers imposed by the Cu(111) substra te, are important factors when it comes to a quantitative comparison betwee n theory and experiment.