ALKALI-METAL PLASMONS, PSEUDOPOTENTIALS, AND OPTICAL SUM-RULES

Starting from recent experimental and theoretical results on the optic al absorption of lithium clusters, we reexamine some effects of the an gular-momentum dependence of tine electron-ion interaction, a necessar y ingredient of accurate valence-only atoms. Our theoretical results a re compared to a variety of optical data for alkali-metal atoms, clust ers, and bulk solids, and illustrate interesting aspects of the jelliu m approximation and of optical sum rules, when based on first-principl es pseudopotentials.