Transition-metal (TM)-doped boron clusters have received considerable attention in recent years, in part, because of their remarkable size-dependent structural and electronic properties. However, the structures of medium-sized boron clusters doped with TM atoms are still not well-known because of the much increased complexity of the potential surface as well as the rapid increase in the number of low-energy isomers, which are the challenges in cluster structural searches. Here, by means of an unbiased structure search, we systematically investigated the structural evolution of medium-sized tantalum-doped boron clusters, TaB (n = 10-20). The results revealed that TaB (n = 10-15) clusters adopt half-sandwich molecular geometries, with the notable exception of TaB, while for n = 16-18 and 19-20, the lowest-energy clusters are characterized by drum-type geometries and tubular molecules with two B atoms on the top, respectively. Good agreement between the calculated and experimental photoelectron spectra strongly support the validity of our global minimum structures. Molecular orbital and adaptive natural density partitioning analyses indicate that the enhanced stability of half-sandwich TaB is due to the strong interaction of the Ta atom (5d orbitals) with surrounding B atoms (2p orbitals) and σ B-B bonds in the B moiety.

We performed systematic structure searches for low energy structures of neutral and singly charged niobium-doped silicon clusters NbSi n Q (n = 2−20; Q = 0, ± 1) by means of the CALYPSO structure searching method. A large population of low energy clusters is collected from the unbiased structure search. Subsequent geometry optimizations using density-functional theory with the B3LYP exchange-correlation functional are carried out to determine structural patterns and relative stabilities of various low energy candidates for Nb-doped silicon clusters. Based on the calculated binding energies along with measured photoelectron spectroscopy data, we are able to confirm that our lowest energy structures are the true minima. It is shown that the localized position of the Nb impurity atom in NbSi n 0/±1 clusters gradually moves from the convex capping position, to surface-substituted, to the concave, and in the end to the encapsulated state as the number of Si atoms increases from 2 to 20. The lowest energy isomer of both neutral and anionic NbSi 12 cluster is very stable in a high-symmetry endohedral D 6h structure in which the Nb atom is placed at the center of a regular hexagonal prism of Si atoms. This makes it an attractive building block for cluster-assembled materials.

Sodium is one of the best examples of a free-electron-like metal and of a certain technological interest. However, an unambiguous determination of the structural evolution of sodium clusters is challenging. Here, we performed an unbiased structure search among neutral and anionic sodium clusters in the medium size range of 10-25 atoms, using the Crystal structure AnaLYsis by Particle Swarm Optimization (CALYPSO) method. Geometries are determined by CALYPSO structure searches, followed by reoptimization of a large number of candidate structures. For most cluster sizes the simulated photoelectron spectra of the lowest-energy structures are in excellent agreement with the experimental data, indicating that the current ground-state structures are the true minima. The equilibrium geometries show that, for both neutral and anionic species, the structural evolution from bilayer structures to layered outsides with interior atoms occurs at n = 16. A novel unprecedented honeycomb-like structure of Na cluster with C symmetry is uncovered, which is more stable than the prior suggested structure based on pentagonal structural motifs.

The structural and electronic properties for the global minimum structures of medium-sized neutral, anionic and cationic Sinμ (n = 20–30, μ = 0, −1 and +1) clusters have been studied using an unbiased CALYPSO structure searching method in conjunction with first-principles calculations. A large number of low-lying isomers are optimized at the B3PW91/6-311 + G* level of theory. Harmonic vibrational analysis has been performed to assure that the optimized geometries are stable. The growth behaviors clearly indicate that a structural transition from the prolate to spherical-like geometries occurs at n = 26 for neutral silicon clusters, n = 27 for anions and n = 25 for cations. These results are in good agreement with the available experimental and theoretical predicted findings. In addition, no significant structural differences are observed between the neutral and cation charged silicon clusters with n = 20–24, both of them favor prolate structures. The HOMO-LUMO gaps and vertical ionization potential patterns indicate that Si22 is the most chemical stable cluster, and its dynamical stability is deeply discussed by the vibrational spectra calculations.

Enormous progress has been made in catalytic oxidation reactions involving nanosized gold particles. However, the reaction mechanism of O2 with neutral gold clusters remains complicated. Here, we have performed an unbiased structure search for Au n Q and Au n O2 Q (n = 2–10, Q = 0, −1) clusters by means of CALYPSO structure searching method. Subsequently, the lowest-energy candidate structures were fully optimized at the B3PW91/Au/LANL2DZ/O/6-311+G­(d) level of theory to determine the global minimum structures. Based on the ground-state structures of Au n – and Au n O2 – (n = 2–10), we have simulated the photoelectron spectra (PES) using time-dependent density functional theory. The good agreement between simulated PES and the corresponding experimental data suggest that the current ground-state structures are the true minima. The locally maximized value of the adsorption energy in Au5O2, where the unpaired electron of Au5 can transfer to O2, makes it the most promising candidate of the chemisorbed complex. A comprehensive analysis of molecular orbitals and chemical bonding of the Au5O2 cluster reveals that O2 can be chemisorbed onto the neutral Au5 cluster.