Quenching of the Size Effects in Free and Matrix-Embedded Silver Clusters

The surface plasmon energy of silver clusters is investigated in the framework of the time-dependent local density approximation. The results are in good agreement with experimental data on free ${\mathrm{Ag}}_N^{+}$ clusters and on ${\mathrm{Ag}}_N$ clusters embedded in solid argon and alumina. The size effects are weak and very sensitive to the matrix, the porosity at the interface, and the cluster charge. It is shown that the core-electron contribution to the metal dielectric function is mainly responsible for the quenching of the size effects in the optical response.