A theoretical investigation of the structural and electronic properties of 55-atom nanoclusters: The examples of Y-Tc and Pt.

Several studies have found that the Pt55 nanocluster adopts a distorted reduced core structure, DRC₅₅, in which there are 8-11 atoms in the core and 47-44 atoms in the surface, instead of the compact and high-symmetry icosahedron structure, ICO₅₅, with 13 and 42 atoms in the core and surface, respectively. The DRC structure has also been obtained as the putative global minimum configuration (GMC) for the Zn₅₅ (3d), Cd₅₅ (4d), and Au₅₅ (5d) systems. Thus, the DRC₅₅ structure has been reported only for systems with a large occupation of the d-states, where the effects of the occupation of the valence anti-bonding d-states might play an important role. Can we observe the DRC structure for 55-atom transition-metal systems with non-occupation of the anti-bonding d-states? To address this question, we performed a theoretical investigation of the Y₅₅, Zr₅₅, Nb₅₅, Mo₅₅, Tc₅₅, and Pt₅₅ nanoclusters, employing density functional theory calculations. For the putative GMCs, we found that the Y₅₅ adopts the ICO₅₅ structure, while Nb₅₅ and Mo₅₅ adopt a bulk-like fragment based on the hexagonal close-packed structure and Tc55 adopts a face-centered cubic fragment; however, Zr₅₅ adopts a DRC₅₅ structure, like Zn₅₅, Cd₅₅, Pt₅₅, and Au₅₅. Thus we can conclude that the preference for DRC₅₅ structure is not related to the occupation of the anti-bonding d-states, but to a different effect, in fact, a combination of structural and electronic effects. Furthermore, we obtained that the binding energy per atom follows the occupation of the bonding and anti-bonding model, i.e., the stability of the studied systems increases from Y to Tc with a small oscillation for Mo, which also explains the equilibrium bond lengths. We obtained a larger magnetic moment for Y₅₅ (31 μB) which can be explained by the localization of the d-states in Y at nanoscale, which is not observed for the remaining systems (0-1 μB). [ABSTRACT FROM AUTHOR]