中文摘要：

采用二阶微扰理论MP2、密度泛函B3LYP方法和含时密度泛函TD．B3LYP方法分别优化了TiO2分子的基态1A1和六个激发态1B2、3B2、1B1、3B1、1A2和2A2的几何结构．1A1、1B2、3B2、1B1和3B1具有弯曲几何结构，1A2和3A2具有线性对称结构．我们发现激发态1B2．3B2、1B1和3B1键偶极矩的数值大小顺序和相应的键角大小顺序完全一致．另外，采用完全活化空间自洽场（CASSCF）CASSCF（6，6）、CASSCF（8，8）、多参考组态相互作用（MRCI）和含时密度泛函TD-B3LYP计算了TiO2分子各激发态的垂直激发能和绝热激发能．对1B2、3B2和1B1三个态，MRCI，CASSCF（6，6）计算的垂直激发能和绝热激发能与已有的实验值最接近．对其他三个激发态3B1、1A2和3A2，计算的激发能和文献报道的激发能计算值基本一致．最后，还计算了TiO2分子的基态和激发态的偶极矩．对1A1和1B2态，偶极矩的计算值与已有的实验值相吻合．采用原子偶极矩校正的HirshfeId布居方法计算了TiO2分子在1A1、1B2．3B2、1B1和3B1态时各原子的电荷。发现从基态到激发态偶极矩的变化与电荷从氧原子向钛原子的转移有关．整个计算中还考察了基函数CC—pVDZ、CC-pVTZ和CC—pVQZ对计算结果的影响．

英文摘要：

The geometries of the ground and excited states of titanium dioxide, 1A1, 1B2, 3B2, 1B1, 3B1, 1A2, and 3A2 have been optimized using Mller-Plesset second-order perturbation theory, density functional theory B3LYP, 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 of 1B2, 3B2, 1B,, 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-B3LYP. For IB2, 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-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 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.