Quantum Size Effects in Equilibrium Lithium Ultrathin Layers

摘要

The existence and extent of quantum size effects in simple metal ultrathin filmsare studied by a systematic local-density, all-electron, full-potential calculation of the cohesive properties of v layers of hexagonal Li, with v = 1, 2, 3, 4, and 5. By v = 5, there is clear convergence of the a lattice parameter to very nearly the calculated crystalline value and those with a minimal interior or none at all. Equally clear stability of the interplanar spacings occurs at distinctly noncrystalline values. The cohesive energies of the 3, 4, and 5 layers are closely clumped at about 87% of the crystalline value. As the 2 and 1 layers are substantially less bound, both the cohesive properties and the inner interplanar spacing suggest a different grouping than suggested by the a lattice parameter. Rough extrapolation of the slowly increasing cohesion with v suggests that approx. = 20 would be needed to achieve even 90% of the crystalline cohesive energy. The calculated surface energies do not exhibit any strong size effect, in striking contrast to Al films.