DFT study of bimetallic palladium-gold clusters Pd(n)Au(m) of low nuclearities (n + m ≤ 14)

Bimetallic palladium-gold Pd(n)Au(m) clusters of low nuclearity (n + m ≤ 14) are studied using the density functional theory at B3LYP level with a Lanl2DZ pseudopotential to understand the evolution of various structural, electronic, and energetic properties as a function of size (n + m) and composition (n/m) of the system. The potential energy surfaces have been explored for many different structures, and the minima obtained were then collected and used as a starting point for comparing the selected properties. Theoretical results show a logical evolution of the properties depending on the size and the composition of the system. Pd(n) clusters clearly prefer 3D structures while Au(m) clusters favor planar configurations. The geometry of the bimetallic Pd(n)Au(m) clusters mainly depends on their composition, i.e., clusters enriched in palladium atoms prefer 3D structures while increasing gold contents promotes planar configurations with deviation from planarity near Pd centers. Regarding the electronic properties, NBO analysis reveals that the unique closed-shell electronic structure of Pd atoms (4d(10)) requires a (4d → 5s) promotion to form stable bonds. In contrast, the half-occupied Au 6s AO implies effective Au-Au interaction and the electronic structure of Au atoms remains almost unchanged upon formation of bimetallic bonds. Consequently, clusters enriched in palladium atoms have spin multiplicities that increase with the cluster size while clusters enriched in gold atoms maintain the lowest possible spin multiplicity. Finally, the stability of these systems shows a synergic gain in cohesion for mixed Pd(n)Au(m) clusters compared to their monometallic Pd(n) and Au(m) counterparts. The maximal stabilization effect corresponds to n ≈ m, compositions for which the number of mixed Pd-Au bonds is maximized.