ENERGY-LOSS SPECTRA AND PLASMON DISPERSIONS IN ALKALI-METALS - NEGATIVE PLASMON DISPERSION IN CS

We present ab initio calculations of the energy loss spectra and plasm on dispersions of the alkali metals Na, K, Rb, and Cs within the rando m phase approximation, including band structure effects and core elect rons as well as local field effects, due to inhomogeneity in the induc ed charge density. Band structure effects an found to cause a negative dispersion in Cs.