Geometries, electronic structures, and vibrational spectra of a series of small niobium clusters Nb n (n ) 2-6) and their cations and anions are reinvestigated with DFT calculations with cc-pVaZ-PP basis sets. CCSD(T) calculations are also carried out for relative energies. In each cluster, different lower lying states are close in energy or quasidegenerate. Stable Nb n clusters prefer high coordination state and 3D shape. Clusters with an odd number of electrons usually have a doublet ground state (except for Nb 2 +). Neutral and cationic clusters with an even number of electrons tend to possess a triplet ground state, with an exception for Nb 4 (T d , 1 A 1 ). For anions, a competition between low and high spin manifolds is observed. Due to the closed electronic shells, the systems possessing 10 (Nb) and 20 valence electrons (Nb 4 ) are observed to be more thermodynamically stable than their neighbors. Electron affinities and ionization energies are reevaluated. In particular, new assignments for the vibrational spectra of the Nb 5 and Nb 6 systems are proposed on the basis of a comparison of calculated results with available experimental data.

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Structural evolution and stability pattern of pure neutral gold clusters Au n in the small size range of n = 20–30 are examined using density functional theory (DFT) calculations. The equilibrium geometries are either confirmed or determined, and some new ground state structures are identified. The most stable configurations of Au21–Au23 sizes are formed by adding extra gold atoms to the highly stable pyramidal structure of Au20, while flat-cage shapes are the best candidates for the global minima of both Au24 and Au25. For larger sizes of n = 26–30, pyramidal motifs tend to dominate the lower-lying population rather than tubular conformations as previously reported. The energy gaps, excitation energies, and exciton binding energies are also computed to test out the performance of the computational methods employed. Accordingly, a density functional with long-range exchange effects is highly recommended to quantitatively investigate both the ground and excited states of pure gold clusters.

Geometric and electronic structures, vibrational properties, and relative stabilities of niobium clusters Nb(n), n = 7-12, are studied using both DFT (BPW91 and M06 functionals) and CCSD(T) calculations with the cc-pVnZ-PP basis set. In each cluster, various lower-lying states are very close in energy in such a way that the ground state cannot be unambiguously established by DFT computations. Nb clusters tend to prefer the lowest possible spin state as the ground state, except for Nb(12) ((3)A(g)). The optimal structure of the cluster at a certain size does not simply grow from that of the smaller one by adding an atom randomly. Instead, the Nb clusters prefer a close-packed growth behavior. Nb(10) has a spherically aromatic character, high chemical hardness and large HOMO-LUMO gap. Electron affinities, ionization energies, binding energy per atom, and the stepwise dissociation energies are evaluated. Energetic properties exhibit odd-even oscillations. Comparison with experimental values shows that both BPW91 and M06 functionals are reliable in predicting the EA and IE values, but the BPW91 is deficient in predicting the binding and dissociation energies. We re-examine in particular the experimental far IR spectra previously recorded using the IR-MPD and free electron laser spectrometric techniques and propose novel assignments for Nb(7) and Nb(9) systems. The IR spectra of the anions are also predicted.