Jahn-Teller effect with rigid octahedral rotations in perovskites

We consider rigid rotation and tilting of the anion octahedra around the transition metal ions in AB O 3 perovskites from the viewpoint of the Jahn -Teller problem and study the effect of the crystal field of the nearest A and B ion cages on the single electron spectrum of the central transition metal B ions. While the crystal field of the octahedra, which creates degenerate manifolds e g and t 2 g , does not change with such rigid rotations, the field of A and B cages deforms significantly from the ideal octahedral field in a way that leads to sizable splittings in these manifolds. The lowering of the ground state energy of a given many -electron configuration due to these splittings can thus be an important driving force behind the octahedral rotations and associated structural transformations. We find that the size of the splitting and the order of the orbitals are determined by a competition between the A and B cages, as well as a competition between the tilt and rotation angles.