An RPA-LDA treatment of density fluctuations in the alkali metals Na and Cs

Abstract

We calcul~te the density fluctuation spectra of the alkali metals Na and Cs in the RPA approximation. using KKR band structure data, The Coulomb part of the K mabix is augmented by a local exchange and wmlation term derived from the LDA. In the case of Na we find well defined plasmon excitations in the wave vector range below qc 5 0.5 (du) whose positions and widlhs are in reasonable agreement with experiment. In accordance with the features of its band shllcture the density response of Cs is more complicated. Nevertheless we find low-frequency peaks whose positions and widths could be interpreted as plasmon-like excitations.