Density fluctuations in molten lithium: inelastic x-ray scattering study

New inelastic x-ray scattering experiments have been performed on Liquid li thium at two different temperatures: T = 475 K (slightly above the melting point) and 600 K. Taking advantage of the absence of any kinematical restri ction and incoherent contribution, and pushing the instrumental resolution up to 1.5 meV, it was possible to perform an accurate investigation of the dynamic structure factor S(Q, E) in the wavevector range from 1 to 110 nm(- 1). For Q smaller than Q(m) similar or equal to 25 nm(-1), the position of the main peak of the static structure factor, a detailed analysis of the li neshapes shows that any picture of the relaxation mechanisms based on a sim ple viscoelastic model must be abandoned. All the spectral features can ins tead satisfactorily be accounted for by including both fast and slow relaxa tion processes. The physical origin of the slow relaxation is associated wi th the structural rearrangement, while the local nature of the fast one is extensively discussed. At larger e-values, a gradual crossover from the str ongly correlated to single-particle dynamics occurs, with an important weig hting provided by quantum effects.