Size Dependence of the Static Polarizabilities and Absorption Spectra of Gold Clusters

We present results for static polarizabilities and absorption spectra for ground state structures of Au$_n$, $n=2-14, 20$, clusters calculated within static and time-dependent density functional theory. The static polarizabilities of the clusters with less than 14 atoms exhibit even-odd oscillations. The polarizabilities of Au$_{14}$ and Au$_{20}$ are noticeably lower. This change in the behavior of static polarizability is correlated with the transition from two-dimensional to three- dimensional structures at $n=14$. The $d$ electrons have a large effect on the optical spectra as they quench the oscillator strengths significantly and are heavily involved in low-energy excitations. The calculated spectra are compared with available experimental data and spectra obtained for Ag$_n$ clusters.\footnote{J. C. Idrobo, S. Ogut, and J. Jellinek, Phys. Rev. B {\bf 72}, 085445 (2005)}