A theoretical search for stable bent and linear structures of low-lying electronic states of the titanium dioxide (TiO2) molecule

Abstract

In this work geometric optimization and potential energy surface (PES) scan for the TiO₂ molecule were carried out to find out possible stable structures by using quantum chemical calculations. The ground state (S₀ 1 ¹A₁) has the only equilibrium with a symmetric bent structure, whereas the linear conformer is unstable. The first singlet excited state (S₁ 1 ¹B₂), on the other hand, possesses two potential minima where one is bent around the Franck–Condon region and the other is linear. The second singlet excited state (S₂ 1 ¹A₂) has only one minimum which is linear, and at which geometry the first two excited states degenerate. Other low-lying singlet and triplet excited states have been investigated accordingly. Among the functionals applied in the present DFT calculations, B3LYP gave results most close to available experimental data, while some recently developed ones including HSE06, ωB97X-D and CAM-B3LYP were not satisfactory for this small system. Ab initio methods such as CASSCF, CASPT2 as well as CCSD-related calculations have been applied, and the latter two showed good results similar to DFT/B3LYP.