Extended Thomas-Fermi molecular dynamics of sodium clusters

We describe a semiclassical molecular-dynamics procedure suitable for charged or neutral clusters of sodium containing up to several hundred atoms. The charged liquid drop energy parameters of the model are extracted, and shown to be in good agreement with empirically inferred values. Vertical ionization energies are also found to be in good agreement with experiment. We find that the time-averaged ionic density becomes jelliumlike with a diffuse surface when the cluster is liquid, and discuss the time-averaged net charge of charged clusters. Clusters from size 8 and up an found to have collective ionic monopole oscillations at a sharp frequency close to that predicted by a compressible liquid drop model. Also, low-frequency shape oscillations occur at frequencies consistent with an incompressible liquid drop model. We discuss the temperature dependence of the surface energy predicted by the model.