Structural, electronic, magnetic and optical properties of icosahedral silver-nickel nanoclusters

We present a systematic study of the structural, electronic, magnetic and optical properties of icosahedral bimetallic Ag(13-p) Ni-p (p <= 6) clusters in the gas phase investigated in the framework of density functional theory (DFT and TDDFT). In the most-stable structures, the central position is found to be occupied by a nickel atom. The evolution of spin-multiplicities and local atomic spin densities with Ag/Ni composition are discussed. The evolution of the optical properties with the Ag/Ni composition and the spatial positions of Ni atoms are analysed. An interpretation of spectroscopic patterns in terms of contribution from s- and d-type excitations is also given. In particular the d-electrons of nickel atoms are found to play a crucial role in the optical transitions of Ni-rich systems. Finally, our theoretical spectra are compared to the experimental ones for large Ni-core/Ag-shell clusters (about 2-5 nm in size).