SELF-COMPRESSION OF METALLIC CLUSTERS UNDER SURFACE-TENSION

The stabilized jellium model is used to explore the physics of self-co mpression for spherical clusters of simple-metal atoms. Within the con tinuum or liquid drop model, strong compression of the interior ionic density of a small cluster (with respect to the bulk density) results from cooperation between surface tension and surface suppression of th e elastic stiffness. The latter effect is due to the large negative va lue of sigma'', the second derivative of surface tension with respect to uniform strain. Self-compression also renormalizes the effective cu rvature-energy coefficient, and contributes to the asymptotic (large-r adius) size effect on the ionization energy. A quantum-mechanical calc ulation of interior density as a function of electron number displays small shell-structure oscillations around the average behavior predict ed by the liquid drop model. Numerical results are presented for clust ers of Al, Na, and Cs. For compact 6-atom clusters of these metals, pr edicted bond lengths are smaller than their bulk values by 10%, 6%, an d 4%, respectively.