Spectrum of collective excitations in liquid metals

The delayed ionic density–density Green's function and dielectric permittivity of simple liquid metals are considered in terms of the pseudopotential of electron–ion interaction. This approach is used to study the spectrum of collective excitations $\omega(k)$ and its position with respect to the maximum of the ionic dynamic structural factor. Numerical calculation for liquid rubidium shows r that the excitation is well determined in the region $k \lesssim 1$ Å$^{-1}$ where there is f deviation from the acoustic dispersion curve.