Another look at structure of gold clusters Aun from perspective of phenomenological shell model

Abstract

Geometric, energetic and electronic properties of Aun clusters, n = 2–20 are determined using DFT calculations (BB95/cc-pVTZ-PP). Global equilibrium structures were confirmed or found, and the growth mechanism was established. Au-clusters prefer 2D-geometries up to Au₁₁ and are generated from the lowest-lying isomer of the smaller size by adding an extra gold atom. Transition from an oblate form to a pyramid is observed at Au₁₇. Aun containing 17–20 atoms favor tetrahedral evolution by adding atoms to the Frank-Kasper 16-vertex. Binding energy per atom, second-order difference of energy, and one-step fragmentation energy show that Au6 and Au₂₀ have high thermodynamic stability. Their valence electrons of generate magic numbers that can be understood using the phenomenological shell model. Due to Jahn-Teller effect, Au₁₆ is characterized by oblate structure whereas the anion Au₁₆-exhibits Frank-Kasper form.