Density dependence of the plasmon dispersion in alkali metals

We investigate the role of electron correlations on the plasmon dispersion in alkali metals using a sum rule approach. The single pair contribution to the low-energy part of the excitation spectrum is calculated in the framework of the Landau theory of Fermi liquids and used to estimate the plasmon contribution to the compressibility sum rule. The plasmon contribution to the f-sum rule is calculated employing a non-local effective interaction (g-matrix) recently proposed in the literature. The analysis accounts for the strong density dependence of the dispersion coefficient alpha exhibited by experimental data. The average energy of multipair excitations is also estimated.