Density Functional Study of Neutral and Charged Silver Clusters Agn with n=2-22. Evolution of Properties and Structure

Geometries and electronic properties of neutral Ag-n, cationic Ag-n(+), and anionic Ag-n(-) silver clusters with n = 2-22 were investigated by density functional theory (DFT) with M06 functional. For neutral clusters, transition from planar to "empty cage" structure occurs at n = 7, "empty cage" to "cage with one Ag atom" at n = 18, and to "cage with two Ag atoms" at n = 22. For lowest energy Ag-n, clusters, Ag-8 and Ag-18 show lowest polarizability due to closed-shell valence electron configurations 1S(2)/1P(6) and 1S(2)/1P(6)/1D(16). High stability of Ag-8 is manifested in small dissociation energies of Ag-9 to Ag-8 plus Ag-1, and Ag-10 cluster to Ag-8 plus Ag-2. Cluster Ag-20 with configuration 1S(2)/1P(6)/1D(10)/2S(2) is stable due to low dissociation energy of Ag-21 to Ag-1, and Ag-22 to Ag-2. Cationic clusters with even n namely Ag-10(+) (9 valence electrons), Ag-16(+) (15 valence electrons), and Ag-22(+) (21 valence electrons) dissociate to Ag-1, and closed-shell Ag-9(+) (1S(2)/1P(6)), Ag-15(+) (1S(2)/1D(10)/2S(2) and Ag-21(+) (1S(2)/1P(6)/1D(10)/2S(2)). For odd n, Ag-11(+) and Ag-17(+) dissociate to Ag-2 and closed-shell Ag-9(+) and Ag-15(+). For anionic clusters Ag-n(-) cohesion energy E-coh and binding energy (BE) show maxima at n = 7 and n = 17 due to stable Ag-7(-) and Agr(17)(-) clusters. Small Ag-n(-) clusters (n = 4-11) with even n (except n = 8) have lower dissociation energy for loss of Ag-1 while those with odd n have lower dissociation energy for loss of Ag-2. For n = 12-22, all clusters have lower dissociation energy for loss of Ag-1.