Density-functional study of impurity-related DX centers in CdF2

We have studied computationally the CdF2 crystal doped with Al, Ga, In, Sc and Y impurities, using the density-functional theory and the ultrasoft pseudopotential method. In particular, we focus on the bistability behavior of the dopants. The formation energies, ionization levels and spatial configurations are calculated. For bistable donor configurations (DX centers), the overlap populations and energy barriers are also estimated. The results obtained for the DX centers associated with Ga and In atoms in the negative charge state are in a good agreement with previous works. We predict the existence of bistability in the case of the Sc-doped CdF2. In all the investigated cases for the DX centers we find an antibonding state between the impurity and the nearest Cd atoms.