THEORETICAL STUDY ON THE STRUCTURES AND GROWTH MECHANISMS OF Ag-RICH CLUSTERS: Ag(Ag2S)n AND Ag2(Ag2S)n (n=1-6)

The Ag-rich clusters Ag(Ag2S)(n) and Ag-2(Ag2S)(n) (n = 1-6) are studied by the genetic algorithm combined with the density functional theory method. The PBE0/Lanl2tz(Ag)/6-311G(d,p)(S) method is used to optimize the structures. The global minimum structures, HOMO and LUMO frontier orbitals, and increment mechanisms of the clusters are investigated. The S-Ag-S unit is present in the structure when n > 1 for Ag(Ag2S)(n) and Ag-2(Ag2S)(n) (n = 1-6) clusters. The triangular Ag3S3 unit is found to be an elemental building block to construct Ag(Ag2S)(n) and Ag-2(Ag2S)(n) (n = 3-6) clusters. The S-Ag-Ag-S unit is present in the structures of Ag(Ag2S)(5) and Ag(Ag2S)(6) clusters. Beginning from Ag(Ag2S), the increment progress is exothermic when one Ag2S molecule or Ag atom is added to the molecule. The structural evolution of the studied clusters follows an edge-to-face growth mechanism. As the clusters increase, the structures evolve from open to cage ones.