Quantum size effect in Pb(100) films: Role of symmetry and implications for film growth

We show from density-functional calculations that Pb(100) thin films exhibit quantum size effect with a bilayer periodicity in film energies, film relaxations, and work functions, which originate from different symmetry of the stacking geometry of odd and even layer films. This symmetry-driven quantum size effect on the film energy could allow for growth of magically thick even-layer Pb(100) films on an appropriate substrate. Furthermore, it is found that the quantum well states in a simple metal film can be classified into sigma-bonded and pi-bonded states, which quantize independently.