| Clusters are particularly interesting research fields because the properties of materials can be designed by exploring the enormous variability in the size, shape, and composition of constituent clusters. Fabrication of cluster-assembled materials depends upon finding a suitable building block for a cluster that is chemically stable and interacts weakly with each other. In this paper, structural and electronic properties of the neutral TaSin (n=l-13, 1.6) clusters, charged TaSin+ (n=l-13, 16) clusters and Irn (n=2-13) clusters are investigated computationally by the relativistic density functional method with generalized gradient approximation.Stimulated by Hiura's experimental findings, the geometric structures, stabilities, electronic and bonding properties of the neutral TaSin and charged TaSin+ (n=1-13, 16) clusters are systematically investigated one after the other, the most stable structures and the corresponding evolutional rule of the TaSin clusters are obtained. The results indicate that the most stable structure of TaSin (n=1-6) clusters keeps the similar framework as the most stable structure of Sin+1 clusters except for TaSi3 cluster. The tantalum atom in the lowest-energy TaSin (n= 1-11) isomers occupies a gradual sinking site, while TaSi12 is a Ta-encapsulating geometry with D6h symmetry, so we can predict the tantalum atom in the most stable TaSin (n≥12) clusters preferring trapping into silicon cage, which is proved by the fact that the most stable TaSin is the C2v cage-like structure and the most stable TaSi16 is a slightly distorted C4v fullerene-like geometry. Compared with the neutral TaSin, clusters, most of the corresponding TaSin+ structures keep basically similar frameworks, while the atomic averaged binding energies and the gaps between the highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO-LUMO gaps) of most TaSin+ clusters universally increase, which indicates that the stabilities of the TaSin+ clusters have been proved simultaneously as compared with the corresponding neutrals, especially obvious for n=4 and 6 clusters, where the serious deformations ingeometries are found. The findings can explain Hiura's experimental result and indicate that the effects of the positive charge on TaSin cluster are stronger for electronic levels than geometric structures. In addition, the net Mulliken and Hirsheld populations of the tantalum atom in the TaSin or TaSin+ (n=1-1 l)clusters are positive that shows the charge transfer being performed from tantalum atom to silicon atoms, but it is not so for n≥12 clusters. Furthermore, the discussions on the contributions by the d orbitals of tantalum atom to the HOMO and LUMO show that the reactive activity of the d orbitals gradually decrease as the number of silicon atoms goes up.Iridium clusters with up to 13 atoms are studied systematically using ab initio relativistic density functional method combined with molecular dynamics simulation. Prism and square bipyramid structural growth patterns are found in the low-lying geometries. The lowest-energy clusters adopt hollow prism structures up to 12, while Ir13 is an amorphous structure. For the lowest-energy iridium clusters, the size-dependences of the fragmentation energies and second order difference of energies show strong odd-even alternative behaviors, at the same time, both the vertical ionization potentials and electron affinities show odd-even oscillation features between n=4 and n=13. These indicate that the even-numbered Irn clusters are relatively more thermodynamic stable than the neighboring odd-sized ones. Except for Ir3(0.42eV), Ir4 with Td (0.50eV), and Ir5 with D3h(0.40eV), the HOMO-LUMO gaps of all other clusters are below 0.3eV, indicating these clusters are chemical active. The size-dependence of the averaged magnetic moments shows an antiferromagnetic order in the lowest-energy clusters. The Irg cluster with regular cube geometry is found to be very stable and nonmagnetic.
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