Dynamic properties of liquid cesium near the melting point: A molecular-dynamics study

We present results of a molecular-dynamics study on liquid cesium, just above the melting point; i.e., we have performed a computer experiment on exactly the same system that was studied recently in a very accurate neutron-scattering experiment by Bodensteiner et al. In this simulation the interaction of the cesium atoms is based on an Ashcroft empty-core pseudopotential; the total simulation length extends over 100 000 time steps, i.e., 8×${10}^{\mathrm{-}10}$ s real time. Both static and dynamic structure factors are in very good agreement with experimental results: as in the experiment, we also get—within very good accuracy—a positive dispersion relation. However, concerning propagating sound modes beyond the main peak in S(q) (q≥${\mathit{q}}_{\mathit{p}}$∼1.4 Å) we cannot find sufficient evidence for their existence. Analysis of the transverse current correlation function shows that the corresponding decay mechanism is built up by two relaxation processes (a fast binary one and a slow collective one); starting from ∼1 A${\mathrm{̊}}^{\mathrm{-}1}$ the latter one is completely extinguished. The correlation functions are fitted to hydrodynamic and memory-function models that contain generalized thermodynamic and elastic quantities as parameters. In several cases—if statistics allows—the true physical values can be recovered; then agreement with experimental values is quite satisfactory (differences of 10–15 % are observed).