Tuning the Electronic Structure of Anatase Through Fluorination

A highly fluorinated anatase lattice has been recently reported, providing a new class of materials whose general chemical formula is Ti(1-x)□(x)X(4x)O(2-4x) (X(-) = F(-) or OH(-)). To characterise the complex structural features of the material and the different F environments, we here apply a computational screening procedure. After deriving a polarisable force-field from DFT simulations, we screen in a step-wise fashion a large number of possible configurations differing in the positioning of the titanium vacancies (□) and of the fluorine atoms. At each step only 10% of the configurations are retained. At the end of the screening procedure, a configuration is selected and simulated using DFT-based molecular dynamics. This allows us to analyse the atomic structure of the material, which is strongly disordered, leading to a strong decrease (by 0.8 eV) of the band gap compared to conventional anatase.