Alkali-metal plasmons, pseudopotentials, and optical sum rules

Starting from recent experimental and theoretical results on the optical absorption of lithium clusters, we reexamine some effects of the angular-momentum dependence of tine electron-ion interaction, a necessary ingredient of accurate valence-only atoms. Our theoretical results are compared to a variety of optical data for alkali-metal atoms, clusters, and bulk solids, and illustrate interesting aspects of the jellium approximation and of optical sum rules, when based on first-principles pseudopotentials.