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The cationic, neutral, and anionic charge states of the B13 cluster are examined through the use of density functional theory. Several different isomers are studied and compared with a special emphasis given to the electronic structure of the lowest lying isomers. Included among the isomers are three which have been proposed earlier and a pair of new ones. While no minima that corresponded to a filled icosahedron could be found for the cluster, an intriguing atom-in-a-cage structure was found that is a local minimum on the cationic, neutral, and anionic surfaces. The structure found for the anionic cluster has D 3 h symmetry, and the 12 external boron atoms are arranged as three six-membered rings back-to-back. The planar and quasi-planar structures are seen to be more stable than three-dimensional isomers, but the ordering by stability of the planar and quasi-planar structures changes depending on the charge. Relative energies, selected geometric features, ionization potentials, and electron affinities are reported for these structures and some justification for the differences seen among the isomers is given. The planar structures benefit from π delocalization. In the case of the global minimum of the B13 + cationic cluster this delocalization is reminiscent of aromaticity.

Time-dependent density-functional theory (TDDFT) is used to study the excitation energies of the global minima of small Zn(i)O(i) clusters, i = 1-15. The relativistic compact effective core potentials and shared-exponent basis set of Stevens, Krauss, Basch, and Jasien (SKBJ), systematically enlarged with extra functions, were used throughout this work. In general, the calculated excitations occur from the nonbonding p orbitals of oxygen. These orbitals are perpendicular to the molecular plane in the case of the rings and normal to the spheroid surface for 3D clusters. The calculated excitation energies are larger for ringlike clusters as compared to 3D clusters, with the excitation energies of the latter structures lying close to the visible spectrum. The difference between Kohn-Sham eigenvalues of the orbitals involved in the electronic excitations studied have also been compared to the TDDFT results of the corresponding excitations for two approximate density functionals, that is, MPW1PW91 and B3LYP, the latter being more accurate. Moreover, they approach the TDDFT value as the cluster size increases. Therefore, this might be a practical method for estimating excitation energies of large Zn(i)O(i) clusters.

The reaction of Ti + ( 4 F, 2 F) + OH 2 has been studied in detail for both doublet and quartet spin states. The only exothermic products are TiO + ( 2 ∆) and H 2 ; formation of several endothermic products is also examined. An in-depth analysis of the reaction paths leading to each of the observed products is given, including various singlet, triplet, and quartet minima, several important transition states, and a discussion of the two H 2 elimination mechanisms proposed in the literature. The experimentally observed spin-forbidden crossing is given a possible explanation. Throughout this work comparison to experimental results in energetics, reaction products, and suggested mechanisms has been central.

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