Equilibrium geometries of AlnTi (n = 2-24) clusters were studied using density-functional theory with generalized gradient approximation. The resulting geometries showed that the titanium atom remains on the surface of clusters for n < 20 but is endohedrally doped from n = 20. This structural transition confirms the previous experiment results obtained by studying their abilities for argon physisorption (Lang, S. M.; Claes, P.; Neukermans, S.; Janssens, E. J. Am. Soc. Mass Spectrom.2011, 22, 1508). The average bond lengths, coordination numbers, relative stabilities, electronic properties, and other relevant properties were discussed. It was found that the doped titanium atoms strengthen the stabilities of the pure aluminum clusters. The coordination numbers of titanium atoms along with the average Al-Ti bond lengths undergo dramatic increases during the structural transition. The intra-atomic hybridization exists in both Ti and Al atoms, and charge transfer from Al atoms to Ti atom were found in these complexes, which should reflect the strength of Al-Ti interactions. Electronic structure analysis based on the partial density of states reveals stronger Al-Ti interactions for the endohedrally doped structures.

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Geometries and dissociation energies of water molecules on Al(n) (n = 2-25) clusters were investigated using density functional theory with all electron relativistic spin-polarized calculations under the generalized gradient approximation. An extensive structure search was performed to identify the low-energy conformations of Al(n)H(2)O complexes for each size. Optimal adsorption sites were assigned for low-energy isomers of the clusters. Size and site specific dependences were studied for the Al(n)H(2)O complexes in stabilities, geometries, adsorption energies, dissociation energies, Al-O bond lengths, and other characteristic quantities. The stabilities and geometries revealed that H atom in H(2)O is not inclined to bond with Al atoms. The most stable Al(n)H(2)O configurations for each size tend to correspond to the most stable bare Al(n) cluster except of Al(6) and Al(24) clusters. The HO bond lengths increase generally 0.01 Å with respect to the isolated H(2)O in all of the adsorption complexes. The dissociation energy of an isolated H(2)O into HO and H was 5.39 eV, which decreased about two-thirds to the energy range of 0.83-2.12 eV with the help of Al(n) clusters. In spite of the fluctuations, the dissociation energies of Al(n)H(2)O complexes rise with the size increasing as a whole. In addition, we also found that the bare Al(n) clusters with high vertical ionization potentials usually have high dissociation energies of H(2)O in the corresponding adsorption models. The energetically preferred spin-multiplicity of all the odd-n Al(n)H(2)O complexes is doublet, and it is singlet for all the even-n complexes with exception of Al(2)H(2)O which is triplet.

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