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.

We performed an unbiased structure search for low-lying energetic minima of neutral and charged palladium PdnQ (n = 2–20, Q = 0, + 1 and –1) clusters using CALYPSO method in combination with density functional theory (DFT) calculations. The main candidates for the lowest energy neutral, cationic and anionic clusters are identified, and several new candidate structures for the cationic and anionic ground states are obtained. It is found that the ground state structures of small palladium clusters are more sensitive to the charge states. For the medium size Pdn0/+/– (n = 16–20) clusters, a fcc-like growth behavior is found. The structural transition from bilayer-like structures to cage-like structures is likely to occur at n = 14 for the neutral and cationic clusters. In contrast, for the anionic counterparts, the structural transition occurs at Pd13–. The photoelectron spectra (PES) of palladium clusters are simulated based on the time-dependent density functional theory (TD-DFT) method and compared with the experimental data. The good agreement between the experimental PES and simulated spectra provides us unequivocal structural information to fully solve the global minimum structures, allowing for new molecular insights into the chemical interactions in the Pd cages.

The effect of Mg doping on the growth behavior and the electronic properties of aluminum clusters has been investigated theoretically using the CALYPSO (Crystal structure AnaLYsis by Particle Swarm Optimization) method in combination with density functional theory calculations. Compared to pure aluminum clusters, the structure of Mg-doped clusters shows the charming transformation with increasing atomic number. The photoelectron spectra (PES) of the global minima of anionic Al and AlMg (n = 3-20) clusters have been calculated based on the time-dependent density functional theory (TD-DFT) method. The reliability of our theoretical methodology is easily corroborated by the good agreement between the experimental PES and the simulated spectra. Our findings bring forth an ionic bonding with enhanced stability for the AlMg cluster, paired with a surprisingly large HOMO-LUMO gap, as would be expected from the magic number of 20 valence electrons.