Single-particle motion in liquid sodium: Thermal crossover between two dynamical regimes

Several features of single-particle dynamics in liquid Na were investigated by both computer simulation and inelastic neutron scattering at two temperatures: 380 K (close to the melting point) and 900 K (not far from the boiling point). In both cases the system is a rather dense liquid, but the dynamics probed by the self intermediate scattering function are found to reflect entirely different phenomena at the two temperatures, indicating a gradual, thermally-induced crossover from a regime dominated by cage effects and slow structural relaxation to another one characterized by the onset of a vortex pattern around the tagged particle.