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

Several studies have found that the Pt-55 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 Zn-55 (3d), Cd-55 (4d), and Au-55 (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 Y-55, Zr-55, Nb-55, Mo-55, Tc-55, and Pt-55 nanoclusters, employing density functional theory calculations. For the putative GMCs, we found that the Y-55 adopts the ICO55 structure, while Nb-55 and Mo-55 adopt a bulk-like fragment based on the hexagonal close-packed structure and Tc-55 adopts a face-centered cubic fragment; however, Zr-55 adopts a DRC55 structure, like Zn-55, Cd-55, Pt-55, and Au-55. 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 Y-55 (31 mu(B)) 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 mu(B)). (C) 2016 AIP Publishing LLC.