Ab initio simulation of titanium dioxide clusters

Density functional calculations are performed on small neutral and negative ly charged TinO2n clusters, with n=1-3. The relative stability of the vario us isomers results from a subtle competition between ionic and covalent eff ects in the Ti-O bonding, and is affected by the overall charge state of th e cluster. Electron affinities and optical excitation gaps, calculated thro ugh 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, w hich permits a simple interpretation of the computed electron affinities ba sed on the chemical shifts of the deep Ti levels. The trends obtained for b oth the electron affinities and the excitation gaps as a function of n help the identification of the most stable isomers consistent with the experime ntal conditions. (C) 1999 Elsevier Science B.V. All rights reserved.