Size dependence of the static polarizabilities and absorption spectra of Agn (n=2-8) clusters

Static polarizabilities and optical absorption spectra of ground state structures of ${\mathrm{Ag}}_{n}$ clusters $(n=2\char21{}8)$ are investigated from first principles within static and time-dependent density functional theory. The static polarizabilities of the clusters with less than 7 atoms exhibit even-odd oscillations. The polarizabilities of ${\mathrm{Ag}}_{7}$ and ${\mathrm{Ag}}_{8}$ are very close and noticeably lower. This change in the behavior of the static polarizability is correlated with the transition from two-dimensional to three-dimensional structures at $n=7$. The optical spectra calculated within the time-dependent local density approximation indicate sharp excitations in the 3\char21{}5 eV region. These are associated mainly with $s$ electrons, although $d$ electrons also affect the spectra by quenching the oscillator strengths through screening of the $s$ electrons and by getting partially involved in the excitations. The calculated optical spectra are in good agreement with the available experimental data and results from earlier theoretical studies.