First principles study of bimetallic Ni$_{13-n}$Ag$_n$ nano-clusters ($n =$ 0$-$13) : Structural, mixing, electronic and magnetic properties

摘要

Using spin polarized density functional theory (DFT) based calculations,combined with ab-initio molecular dynamics simulation, we carry out asystematic investigation of the bimetallic Ni$_{13-n}$Ag$_n$ nano clusters, forall compositions. This includes prediction of the geometry, mixing behavior,and electronic properties. Our study reveals a tendency towards formation of acore-shell like structures, following the rule of putting Ni in highcoordination site and Ag in low coordination site. Our calculations predictnegative mixing energies for the entire composition range, indicating mixing tobe favored for the bimetallic small sized Ni-Ag clusters, irrespective of thecompositions. The magic composition with the highest stability is found for theNiAg$_{12}$ alloy cluster. We investigate the microscopic origin of core-shelllike structure with negative mixing energy, in which the Ni-Ag inter-facialinteraction is found to play role. We also study the magnetic properties of theNi-Ag alloy clusters. The Ni dominated magnetism, consists of parallelalignment of Ni moments while the tiny moments on Ag align in anti-parallel toNi moments. The hybridization with Ag environment causes reduction of Nimoment.