Structural properties of MeF2 (Me=Ca, Sr, Ba) crystals doped with rare-earth ions RE3+/ RE2+: ab initio route

Abstract

In this paper, we simulated the structural properties of the cubic impurity centers RE3+/RE2+ (RE = Rare earth) in fluorites crystals MeF2 (Me = Ca, Sr, Ba) by ab initio route. Doping fluorite crystals with the rare-earth ion RE3+/RE2+, this replaces the cation Me2+ and determines distortions of the MeF2 crystal lattice near the impurity center. These distortions characterized by radial and angular displacements of anions were investigated by ab initio method. We have employed the MO LCAO approach, in the frame of DFT method as it is implemented in the CRYSTAL17 software for periodic systems, using the hybrid functional PBE0. Since the main contribution to the crystal field on the rare-earth impurity ions comes from its nearest neighbors, the distance “rare-earth ion – ligand” and the radial and angular coordinates of the RE3+/RE2+ ions at several coordination spheres of anions near the impurity centers are calculated. Also, the changes in the local compressibility of the cationic and anionic sublattice next to the impurity ion are determined. The obtained results were discussed, compared with available experimental data and other theoretical results, and the agreement is quite satisfactory.