Static polarizabilities and optical absorption spectra of gold clusters (Aun, n=2-14 and 20) from first principles

Static polarizabilities and optical absorption spectra for the ground state structures of gold clusters (Au-n, n=2-14 and 20) are investigated from first principles within static and time-dependent density functional theory. The static polarizabilities of clusters with less than 14 atoms generally increase as a function of size modulated by even-odd oscillations. The polarizabilities of Au-14 and Au-20 are noticeably lower due to the shape transition from two-dimensional to three-dimensional structures at n=14. The analyses of the optical absorption spectra calculated within the time-dependent local density approximation indicate that the d electrons in Au-n clusters are significantly more involved in low-energy transitions and give rise to more quenched oscillator strengths (by screening the s electrons) than in Ag-n clusters. These stronger effects of the d electrons in the optical properties of Au-n are due to the larger degree of proximity of the s and d levels in the Au atom as compared to the Ag atom, which gives rise to stronger s-(p)-d hybridization in the molecular orbitals of Au-n. The calculated spectra are found to be in good agreement with experimental data and results from earlier studies for the available sizes.