Optical properties of pure and core-shell noble-metal nanoclusters from TDDFT: The influence of the atomic structure

Pseudopotential time-dependent density-functional theory (TDDFT) calculations are carried out to investigate the optical absorption spectra of magic-number noble-metal nanoparticles of 13, 38, 55, 140, and 147 atoms. In particular, we study the differences between isomeric structures such as Ag-13 in both cubic and icosahedral structures. Differences are well visible up to sizes of about 55 atoms, demonstrating the need for proper treatment of the structural details on the atomic level. For the largest sizes of about 150 atoms, our calculations confirm earlier results of TDDFT using a structureless jellium model. In particular, we recover the surface plasmon resonance for silver nanoclusters. The bimetallic Ag32Au6 core-shell cluster displays an intense peak corresponding to the surface-plasmon resonance in the Ag cluster, but the spectrum does not lie between the spectra of the pure Ag-38 and Au-38 clusters. By contrast, a copper core in a Ag38Cu6 cluster leads to a strong damping of this peak.