DFT study of size-dependent geometries,stabilities and electronic properties of Si2Agn clusters: comparison with pure silver clusters

The equilibrium geometric structures, stabilities and electronic properties of Si₂Ag_n (n = 1–8) and pure silver Ag_n (n ≤ 10) clusters have been systematically investigated by using meta-generalised gradient approximation. Due to sp³ hybridisation, the lowest energy structures of Si₂Ag_n clusters for n > 2 favour the three-dimensional structure. The silicon atoms prefer to be located at the surface of the host silver clusters. By analysing the relative stabilities, it is found that the di-bridged structure Si₂Ag₂ isomer is the most stable structure for Si₂Ag_n (n = 1–8) clusters. The highest occupied–lowest unoccupied molecular orbital gaps, exhibiting a pronounced even–odd alternation, indicate that the doped clusters with even number of atoms have enhanced chemical stability than those with odd number of atoms. The results of Wiberg bond indices and electronic localisation function show that the stronger Si–Si and Si–Ag interaction may be the main driving force for the higher stability of Si₂Ag_n clusters.