3d impurities in normal and inverted perovskites: Differences are not explained by ligand field theory

Although the lattice constants of KMgF3 (normal cubic perovskite structure) and BaLiF3 (inverted perovskite) materials differ only by 0.3%, there is a significant difference between the measured cubic field splitting parameters 10Dq for KMgF3:Ni2+ (7800 cm(-1)) and BaLiF3:Ni2+ (8400 cm(-1)). By means of density functional theory calculations, it is shown that such a difference (similar to that observed for Co2+ and Mn2+ impurities) can hardly be understood within the traditional ligand field theory, which ignores the influence of the electrostatic potential V-R(r) exerted by the rest of the lattice ions upon the localized electrons of the NiF64- complex. Although V-R(r) is known to be very flat for a normal perovskite structure, it is shown that this is no longer true for an inverted perovskite. The origin of this significant difference is accounted for by simply considering, for the two cubic lattices, the electrostatic interaction of the two first ion shells around the complex with the electrons in the NiF64- unit. The results of this work emphasize the importance of V-R(r) when comparing the electronic properties of the same transition metal complex but embedded in two lattices that are not isomorphous even if both are cubic.