Understanding Superatomic Ag Nanohydrides

Bulk Ag hydrides are extremely challenging to make even at very high pressures, but they may become stable as the particle size shrinks to the nanometer regime. Here, the formation and electronic structure of Ag nanohydrides are investigated from a superatomic perspective by density functional theory. It is found that as the coverage increases, adsorption energy of hydrogen atoms on Ag₃₈ cluster to form Ag₃₈ H_{2 n} nanohydride (n is from 1 to 15) can be energetically favorable with respect to bare Ag₃₈ and H₂ . Furthermore, the adsorbed hydrogen atoms contribute their 1s electrons to the superatom electron count and behave as a metal instead of a ligand. The electronic structure of the silver nanohydrides follows the superatomic complex model, leading to magic or relatively more stable compositions such as Ag₃₈ H₂ , Ag₃₈ H₂₀ , and Ag₃₈ H₃₀ , which correspond to 40-electron, 58-electron, and 68-electron shell closings, respectively. Angular momentum analyses of the superatomic orbitals suggest a convoluted interaction of geometry, symmetry, and orbital splitting.