Size Dependence of the Optical Response of Spherical Sodium Clusters

Abstract

The optical response of spherical ${{\mathrm{Na}}_j}^{+}$ clusters ($9\le j\le 93$) shows one large maximum at about 2.7 eV. As a function of the inverse cluster radius its peak position and root mean square energy extrapolate linearly, but with different slopes, to the bulk Mie plasmon. The slopes are compared to two theoretical predictions: the static spill-out equation of cluster science and the dynamic screening theory of surface science as generalized to clusters. Good agreement is obtained. The similarity of collective excitations of surfaces and clusters is emphasized.