Hollow polyhedral structures and properties of Ag_2n-1S_n^- (n = 2-11) clusters: A theoretical study

The structures of Ag_2n-1S_n^- (n = 2-11) clusters are obtained by the combination of genetic algorithm (GA) and density functional theory (DFT). All the global minimum structures prefer hollow polyhedral structures, in which S-Ag-S element, triangular Ag₃S₃ and tetragonal Ag₄S₄ units present to stabilize the structures. The S atoms in the structures appear in μ₃-S or μ₄-S form. Adiabatic and vertical electron affinities of the clusters have been obtained, which reveals that they increases as cluster size. Stability analysis shows that Ag₉S₅^- and Ag₁₉S₁₀^- have special stability. The HOMO, LUMO orbitals of the clusters are obtained and the orbital components of them are calculated. The HOMO orbitals are mainly from the p orbitals of S atoms, whereas the s, p and d orbitals of Ag atoms contribute much bigger than the p orbitals of S atoms for LUMO orbitals. The orbital delocalization indexes (ODI) of the HOMOs and LUMOs are calculated, and the small ODIs of the HOMOs and LUMOs for n = 4-10 reveal that these orbitals are highly delocalized. By studying the projected density of states and molecular orbitals of Ag₉S₅^- and Ag₁₉S₁₀^- clusters, it is found that their molecular orbitals have superatomic properties. Superatomic properties play an important role in stabilizing clusters.

This work used combined genetic algorithm and density functional theory (GA-DFT), and PBE0/Lanl2tz(Ag)/6-311G(d,p)(S) method to optimize the structures. Gaussian 16 program, Gauss view 6.0.16 program and Multiwfn 3.8 code are the softwares used.