Structure and optical properties of core-shell bimetallic _Agn Nin clusters: Comparison with pure silver and nickel clusters

We present the structural, electronic, and optical properties of bimetallic Ag_n Ni_n (n≤7) clusters investigated in the framework of the density functional theory (DFT) (DFT and time-dependent DFT). The structure of Ag_n Ni_n clusters is found to be governed essentially by the formation of a Ni-core surrounded by silver atoms. The cohesive energies and the ionization potentials are calculated. The UV-visible absorption spectra of bimetallic clusters are compared to those of pure silver and nickel clusters. 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 in Ni-rich systems.