Structure and Stability of (TiO2)n, (SiO2)n, and Mixed TimSin-mO2n [n=2-5, m=1 to (n-1)] Clusters

Structures, energetics, and vibrational spectra are investigated for small pure (TiO2)(n), (SiO2)(n), and mixed TimSin-mO2n [n = 2-5, m = 1 to (n - 1)] oxide clusters by density functional theory (DFT). The BP86/ATZP level of theory is employed to obtain constitutional isomers of the oxide clusters. In accordance with previous studies, our calculations show three-dimensional compact structures are preferred for pure (TiO2)(n) with Oxo-stabilized higher hexavalent states, and linear chain structures are favored for pure (SiO2)(n) with tetravalent states. However, the herein theoretically first reported mixed TimSin-mO2n oxide clusters prefer either three-dimensional compact or linear chain structures depending upon the stoichiometry of the compound. Vibrational analysis of the important modes of some highly stable structures is provided. Coupled-cluster single and double excitation (with triples) [CCSD(T)] computed energy gaps for the TiO2 dimers compare well with results from previous study. Excitation energies are computed by use of time-dependent (TD) DFT and equation-of-motion coupled-cluster calculations with singles and doubles (EOM-CCSD) for the most stable isomers.