An atom-level ab initio understanding of the structural, energetic, and electronic properties of nanoclusters with diameter size from 1 to 2 nm figures as a prerequisite to foster their potential technological applications. However, because of several challenges such as the identification of ground-state structures by experimental and theoretical techniques, our understanding is still far from satisfactory, and further studies are required. We report a systematic ab initio investigation of the 55-atom metal nanoclusters, (M 55 ), including alkaline, transitional, and post-transitional metals, that is, a total of 42 systems. Our calculations are based on all-electron density functional theory within the Perdew−Burke−Ernzerhof (PBE) functional combined with van der Waals (vdW) correction, spin−orbit coupling (SOC) for the valence states. Furthermore, we also investigated the role of the localization of the d states by using the PBE+U functional. We found a strong preference for the putative PBE global-minimum configurations for the compact Mackay icosahedron structure, namely, 16 systems (Na, Mg, K, Sc, Ti, Co, Ni, Cu, Rb, Y, Ag, Cs, Lu, Hf, Re, Hg), while several systems adopt alternative compact structures such as 6 polytetrahedron (Ca, Mn, Fe, Sr, Ba, Tl) and 10 structures derived from crystalline face-centered cubic and hexagonal close-packed (HCP) fragments (Cr, Nb, Mo, Tc, Ru, Rh, Pd, Ta, W, Os). However, the 10 remaining systems adopt less compact structures based on the distorted reduced-core structure (V, Zn, Zr, Cd, In, Pt, Au), tetrahedral-like (Al, Ga), and one HCP wheel-type (Ir) structure. The binding energy shows a quasi-parabolic behavior as a function of the atomic number, and hence the occupation of the bonding and antibonding states defines the main trends (binding energy, equilibrium bond lengths, etc.). On average, the binding energy of the M 55 systems represents 79% of the cohesive energy of the respective bulk systems. The addition of the vdW correction changes the putative global-minimum configurations (pGMCs) for selected cases, in particular, for post-transitional metal systems. As expected, the PBE+U functional increases the total magnetic moment, which can be explained by the increased localization of the d states, which also contributed to increase the number of atoms in the core region (increase coordination) of the pGMCs. In contrast with the effects induced by the vdW correction and localization of the d states, the addition of the SOC coupling cannot change the lowest energy configurations, but it affects the electronic properties, as expected from previous calculations for 13-atom clusters.

Platinum-based nanoalloys can yield unique properties due to synergistic effects derived from the combination of Pt with one or more transition-metal (TM) species, as well as from the chemical ordering within the particles such as the formation of core–shell PtTM structures. Although several studies have been reported, our atomistic understanding of the key physical and chemical descriptors that lead to the formation and stability of the core–shell structures are not completely understood. Here, we discuss such descriptors to understand the formation and stability of 11 platinum-based nanoalloys through ab initio density functional theory calculations employing 55-atom PtTM model systems. Studying several properties and using the Spearman correlation analysis, we found that the core–shell PtTM nanoalloys are energetically more stable if the surface region is populated by the chemical species with larger atomic radius and lower surface energy, which helps to reduce strain and forms stable structures. For nanoalloys of chemical species with large difference in the electronegativity, the energetic stability is enhanced by the Coulomb attraction between the cationic core and anionic surface derived from charge transfer, which increases the strain on the core and contributes to increase the segregation of large species to the surface region. Thus, the atomic radii, surface energies, and charge transfer play a crucial role in the formation and stability of core–shell PtTM nanoalloys.

From our ab initio investigation, we have improved the understanding of the interaction between Nickel nanoclusters and diatomic molecules, such as CO, NO, and SO, to provide insights into real subnano catalysts.