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

Data-driven stabilization of NimPdn-m nanoalloys: a study using density functional theory and data mining approaches

Green hydrogen, generated through the electrolysis of water, is a viable alternative to fossil fuels, although its adoption is hindered by the high costs associated with the catalysts. Among a wide variety of potential materials, binary nickel-palladium (NiPd) systems have garnered significant attention, particularly at the nanoscale, for their efficacious roles in catalyzing hydrogen and oxygen evolution reactions. However, our atom-level understanding of the descriptors that drive their energetic stability at the nanoscale remains largely incomplete. Here, we investigate by density functional theory calculations the descriptors that drives the stability of the NimPdn-m clusters for different sizes (n = 13, 27, 41) and compositions. To achieve our goals, a large number of trial configurations were generated and selected using data mining algorithms (k-means, t-SNE) and genetic algorithms, while the most important physical-chemical descriptors were identified using Spearman correlation analysis. We have found that core-shell formation, with the smaller Ni atoms lying in the center of the particle, plays a major role in the stabilization of the nanoalloys, and this effect causes the alloys to assume a icosahedral-fragment configuration (as the unary nickel cluster) instead of a fcc fragment (as the unary palladium cluster). However, the core-shell formation in this alloy is unique in that Pd poor compositions exhibit scattered Pd atoms on the surface. As the palladium content increases, this gives rise to the complete Pd shell. This stabilization mechanism is quantitatively supported by the different correlations observed in the number of Ni-Ni and Pd-Pd bonds with energy, in which the latter tends to decrease alloy stability. Furthermore, a notable trend is the correlation between the coordination number of Ni atoms with alloy stabilization, while the coordination of Pd atoms shows an inverse correlation.

Cage doping of Ti, Zr, and Hf-based 13-atom nanoclusters: two sides of the same coin

Transition metal nanoclusters can exhibit unique and tunable properties which result not only from their chemical composition but also from their atomic packing and quantized electronic structures. Here, we introduce a promising family of bimetallic TM@Ti12, TM@Zr12, and TM@Hf12 nanoclusters with icosahedral geometry, where TM represents an atom from groups 3 to 12. Density functional theory calculations show that their stability can be explained with familiar concepts of metal cluster electronic and atomic shell structures. The magnetic properties of these quasispherical clusters are entirely consistent with superatom electronic shells and Hund's rules, and can be tuned by the choice of the TM dopant. The computed cluster atomization energies were analyzed in terms of the elements' cohesive energy, Ecoh, and contributions from geometric distortion, Edis, surface energy, Es, and ionic bonding, Ei. Some clusters have anomalous stability relative to Ecoh + Edis + Es + Ei. We attribute this to superatomic character associated with a favorable atomic and electronic shell structure. This raises the possibility of designing stable superatoms and materials with tailored electronic and magnetic properties.

Intermetallic Differences at CdS-Metal (Ni, Pd, Pt, and Au) Interfaces: From Single-Atom to Subnanometer Metal Clusters

Metal co-catalysts tipped at a photocatalyst surface form a crucial component in the nanoheterostructures designed for the photocatalytic hydrogen evolution reaction. To examine the intermetallic differences and size effects at these interfaces, we use spin-polarized density functional theory to study single-atom, 13-atom, and 55-atom cluster depositions of Ni, Pd, Pt, and Au on the CdS(101̅0) surface. For the single metal atoms, the ground-state configuration was the same site for all of the elements. Analysis of the metal-CdS bonding and of the charge transfers revealed a Ni-Cd bonding complex leading to depletion of electronic charge at the Ni single atom and at deposited Ni clusters, in contrast to charge accumulation observed for the other three metals Pd, Pt, and Au. For scaling up sizes of the metal deposition, six subnanometer cluster types were selected over a wide range of cluster's effective coordination number, and their interfaces were differentiated by charge redistributions, structure and adhesion energies, highest occupied molecular orbital-lowest occupied molecular orbital (HOMO-LUMO) gaps, and Schottky barrier heights. Although all considered clusters are semiconducting in the gas phase, 9 out of 28 clusters became (semi)metallic after deposition on the CdS semiconductor surface. Intermetallic differences and common trends are discussed.

Density functional investigation of the adsorption effects of PH3 and SH2 on the structure stability of the Au55 and Pt55 nanoclusters

Although several studies have been reported for Pt₅₅ and Au₅₅ nanoclusters, our atomistic understanding of the interplay between the adsorbate-surface interactions and the mechanisms that lead to the formation of the distorted reduced core (DRC) structures, instead of the icosahedron (ICO) structure in gas phase, is still far from satisfactory. Here, we report a density functional theory (DFT) investigation of the role of the adsorption effects of PH₃ (one lone pair of electrons) and SH₂ (two lone pairs) on the relative stability of the Pt₅₅ and Au₅₅ nanoclusters. In gas phase, we found that the DRC structures with 7 and 9 atoms in the core region are about 5.34 eV (Pt₅₅) and 2.20 eV (Au₅₅) lower in energy than the ICO model with I_h symmetry and 13 atoms in the core region. However, the stability of the ICO structure increases by increasing the number of adsorbed molecules from 1 to 18, in which both DRC and ICO structures are nearly degenerate in energy at the limit of 18 ligands, which can be explained as follows. In gas phase, there is a strong compression of the cationic core region by the anionic surface atoms induced by the attractive Coulomb interactions (core⁺-surface^-), and hence, the strain release is obtained by reducing the number of atoms in the cationic core region, which leads to the 55 atoms distorted reduced core structures. Thus, the Coulomb interactions between the core⁺ and surface^- contribute to break the symmetry in the ICO₅₅ structure. On the other hand, the addition of ligands on the anionic surface reduces the charge transfer between the core and surface, which contributes to decrease the Coulomb interactions and the strain on the core region of the ICO structure, and hence, it stabilizes a compact ICO structure. The same conclusion is obtained by adding van der Waals corrections to the plain DFT calculations. Similar results are obtained by the addition of steric effects, which are considered through the adsorption of triphenylphosphine (PPh₃) molecules on Au₅₅, in which the relative stability between ICO and DRC is the same as for PH₃ and SH₂. However, for Pt₅₅, we found an inversion of stability due to the PPh₃ ligand effects, where ICO has higher stability than DRC by 2.40 eV. Our insights are supported by several structural, electronic, and energetic analyses.

Evolution of the structural, energetic, and electronic properties of the 3d, 4d, and 5d transition-metal clusters (30 TMn systems for n = 2–15): a density functional theory investigation

Subnanometric transition-metal (TM) clusters have attracted great attention due to their unexpected physical and chemical properties, leastwise compared to their bulk counterparts.