Abstract
The dynamic structure factor, S(Q,E), of liquid lithium (T = 475 K) has been remeasured by inelastic X-ray scattering (IXS) in an extended momentum transfer region (Q = 1.4–110 nm−1) and with improved energy resolution (down to 1.5 meV). These new data on such prototypical simple liquid allow to observe the full evolution with Q from a phonon-like collective mode towards the single-particle dynamics. As a function of Q, one finds: i) at low Q's, a sound mode with a positive dispersion of the sound velocity, ii) at intermediate Q's, excitations whose energy oscillates similarly to phonons in the crystal Brillouin zones, and iii) at high Q's, the S(Q,E) approaches a Gaussian shape, indicating that the single-particle dynamics has been reached.