Geometric Structures, Excitation Energies and Dipole Moments of the Ground and Excited States of TiO<sub>2</sub>

Abstract

The geometries of the ground and excited states of titanium dioxide,1A1,1B2, 3B2,1B1, 3B1,1A2, and 3A2 have been optimized using M ller-Plesset second-order perturbation theory, density functional theory B3 LYP, and time-dependent density functional theory TD-B3LYP methods.1A1,1B2, 3B2,1B1, 3B1, and 3B1 have bent structures, while 1A2 and 3A2 have symmetrical linear structures. The bond angles of1B2, 3 B2,1B1, and 3B1 correlate directly with the magnitudes of the corresponding bond dipole moments. Vertical and adiabatic excitation energies have been computed with complete active space self-consistent field (CASSCF) CASSCF(6,6), CASSCF(8,8), multi-reference configuration interaction (MRCI), and TD-B3 LYP. For1B2,3B2, and 1B1, the excitation energies calculated with MRCI/CASSCF(6,6) are much closer to the experimental values than the results calculated using other methods. For excited states 3B1,1A2, and 3A2, excitation energies calculated with CASSCF(6,6), CASSCF(8,8), MRCI, and TD-B3 LYP are almost consistent with theoretical results available in the literature. Dipole moments of the ground and excited states have been computed with B3 LYP and TD-B3 LYP. The calculated dipole moments of 1A1 and 1B2 agree well with experimental data. The atomic charges of TiO2 in ground and excited states have been calculated with the atomic dipole moment corrected Hirshfeld population method. This calculation revealed that changes of dipole moments from the ground state to the excited states are related to electron transfer from the oxygen atom to the titanium atom. During the above calculations, the influences of the basis sets cc-pVDZ, cc-pVTZ, and cc-pVQZ were also investigated.