Dynamical structure factor in liquid rubidium

The dynamical structure factor S(k, omega ) is studied by using the memory function formalism for the wavenumber k=1.25 approximately 5.0 AA-1 in liquid rubidium. The memory function for the density-density correlation function is expressed in terms of its free part and a polarisation function. For the latter the time dependence is assumed to be Gaussian and S(k, omega ) is calculated by normalising it to the experimental result at omega =0. The line-shape and the full width at half maximum of S(k, omega ) and the frequency at a peak and the peak height of the spectral function of the current-current correlation function are compared with the result of the neutron inelastic scattering measurement. It is found that a single Gaussian is sufficient for large wavenumbers, but that a sum of two Gaussians gives better agreement for the wavenumber near k=2.0 AA-1.