Static electric and optical properties of two coupled noble metal nanoparticles

The static electric polarizability and absorption spectrum of the coupled noble metal (Ag, Au, Cu) cluster-pair are investigated within density functional theory (DFT). The results show that the HOMO–LUMO gap gradually widens with increasing cluster distance D, and the static polarizability exhibits a maximal value as D is near the average bond length of cluster. In the absorption spectrum, the spectral strength is related to electric dipole moments which sensitively rely on D. With the increase of D the low-energy peaks (LEPs) obviously blue shift while the high-energy peaks (HEPs) keep their positions unmoved. The LEPs (HEPs) mostly comes from the transitions between near (far) the HOMO and LUMO energy levels. In these transitions, the low-energy excitations are dominantly contributed by d-electrons, indicating the fact that intense coupling effects can weaken the screen of d-electrons on sp-electrons. By means of the competition mechanism between charge transfer and electron cloud distortion, the spacing dependence behaviors of both electric and optical properties are explained self-consistently.