Density Functional Study of Neutral and Charged Silver Clusters Ag_<i>n</i> with <i>n</i> = 2–22. Evolution of Properties and Structure

Abstract

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, Ag₈ and Ag₁₈ show lowest polarizability due to closed-shell valence electron configurations 1S²/1P⁶ and 1S²/1P⁶/1D¹⁰. High stability of Ag₈ is manifested in small dissociation energies of Ag₉ to Ag₈ plus Ag₁ and Ag₁₀ cluster to Ag₈ plus Ag₂. Cluster Ag₂₀ with configuration 1S²/1P⁶/1D¹⁰/2S² is stable due to low dissociation energy of Ag₂₁ to Ag₁ and Ag₂₂ to Ag₂. Cationic clusters with even n namely Ag₁₀⁺ (9 valence electrons), Ag₁₆⁺ (15 valence electrons), and Ag₂₂⁺ (21 valence electrons) dissociate to Ag₁ and closed-shell Ag₉⁺ (1S²/1P⁶), Ag₁₅⁺ (1S²/1D¹⁰/2S²) and Ag₂₁⁺ (1S²/1P⁶/1D¹⁰/2S²). For odd n, Ag₁₁⁺ and Ag₁₇⁺ dissociate to Ag₂ and closed-shell Ag₉⁺ and Ag₁₅⁺. For anionic clusters Ag_n^-, cohesion energy E_coh and binding energy (BE) show maxima at n = 7 and n = 17 due to stable Ag₇^- and Ag₁₇^- clusters. Small Ag_n^- clusters (n = 4-11) with even n (except n = 8) have lower dissociation energy for loss of Ag₁ while those with odd n have lower dissociation energy for loss of Ag₂. For n = 12-22, all clusters have lower dissociation energy for loss of Ag₁.