Transverse modes in the spectra of density fluctuations of simple liquids

We report the results of transverse and longitudinal current correlation functions evaluated in liquid and amorphous sodium by computer simulation. The analysis of the corresponding spectra allows the evaluation of a dispersion curve position as a function of the wavevector. The results are compared with the experimental findings of Giordano-Monaco (PNAS 107, 21985 (2010)), obtained by new analysis of S(k,ù) measured by inelastic X-Ray scattering in liquid and polycrystalline sodium. A substantial agreement between experimental and computer simulation results is found. We studied also the behaviour of the line width in terms of the wavevector which gives hints for the correct interpretation of the experimental results. An attempt of a theoretical explanation of the whole set of data is performed by making use of the Vibration-Transit theory developed for the study of the dynamical processes in simple liquids.