DENSITY-DEPENDENCE OF THE PLASMON DISPERSION IN ALKALI-METALS

We investigate the role of electron correlations on the plasmon disper sion in alkali metals using a sum rule approach. The single pair contr ibution to the low-energy part of the excitation spectrum is calculate d in the framework of the Landau theory of Fermi liquids and used to e stimate the plasmon contribution to the compressibility sum rule. The plasmon contribution to the f-sum rule is calculated employing a non-l ocal effective interaction (g-matrix) recently proposed in the literat ure. The analysis accounts for the strong density dependence of the di spersion coefficient alpha exhibited by experimental data. The average energy of multipair excitations is also estimated.