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 ext racted, and shown to be in good agreement with empirically inferred va lues. Vertical ionization energies are also found to be in good agreem ent with experiment. We find that the time-averaged ionic density beco mes jelliumlike with a diffuse surface when the cluster is liquid, and discuss the time-averaged net charge of charged clusters. Clusters fr om size 8 and up an found to have collective ionic monopole oscillatio ns at a sharp frequency close to that predicted by a compressible liqu id drop model. Also, low-frequency shape oscillations occur at frequen cies consistent with an incompressible liquid drop model. We discuss t he temperature dependence of the surface energy predicted by the model .