Ab initio simulation of titanium dioxide clusters

Density functional calculations are performed on small neutral and negatively charged Ti(n)O(2n) clusters, with n=1-3. The relative stability of the various isomers results from a subtle competition between ionic and covalent effects in the Ti-O bonding, and is affected by the overall charge state of the cluster. Electron affinities and optical excitation gaps, calculated through total-energy differences, are discussed and compared with recent anion photoelectron data. The excess electron of the negatively charged clusters is mostly localized on titanium with the weakest electrostatic potential, which permits a simple interpretation of the computed electron affinities based on the chemical shifts of the deep Ti levels. The trends obtained for both the electron affinities and the excitation gaps as a function of n help the identification of the most stable isomers consistent with the experimental conditions. (C) 1999 Elsevier Science B.V. All rights reserved.