Trends and Properties of 13-Atom Ag–Au Nanoalloys I: Structure and Electronic Properties

We present a systematic study of the structures and the electronic and magnetic properties of 13-atom Ag–Au nanoalloys, using spin-polarized <i>ab initio</i> calculations based on density functional theory. To this end, we use all possible chemical configurations of four different initial symmetries as starting structures: icosahedra, decahedra, cuboctahedra, and the buckled biplanar (BBP) cluster. Mixing is energetically favored; there is no indication of segregation. We find a general tendency to minimize the number of Au–Au bonds. Many of the clusters undergo strong morphology changes. The resulting structures of lowest energy, independent of the starting geometry, are distorted biplanar clusters. The cuboctahedra are a rather stable local minimum against geometry changes following the introduction of the mixing. All the lowest-energy structures have a Kohn–Sham HOMO–LUMO gap of about 0.2 eV and a total spin of 1 μ_B. Higher total spin values are found for some of the icosahedra and decahedra, but they have an energy much higher than that of the lowest-energy structures of the respective compositions. The quasi-particle gap is about 3.7 eV across the composition range. It does not vary appreciably with the composition and structural details of the clusters