Geometric Structures, Excitation Energies and Dipole Moments of the Ground and Excited States of TiO2

The geometries of the ground and excited states of titanium dioxide, (1)A(1), B-1(2), B-3(2), B-1(1), B-3(1), (1)A(2), and (3)A(2) have been optimized using Moller-Plesset second-order perturbation theory, density functional theory B3LYP, and time-dependent density functional theory TD-B3LYP methods. (1)A(1), B-1(2), B-3(2), B-1(1), B-3(1), and B-3(1) have bent structures, while (1)A(2) and (3)A(2) have symmetrical linear structures. The bond angles of B-1(2), B-3(2), B-1(1), and B-3(1) 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-B3LYP. For B-1(2), B-3(2), and B-1(1), 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 B-3(1), (1)A(2), and (3)A(2), excitation energies calculated with CASSCF(6,6), CASSCF(8,8), MRCI, and TD-B3LYP are almost consistent with theoretical results available in the literature. Dipole moments of the ground and excited states have been computed with B3LYP and TD-B3LYP. The calculated dipole moments of (1)A(1) and B-1(2) 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