Jahn‐Teller distortion, octahedra rotations and orbital ordering in perovskites: KScF3 as a model system.

The KScF 3 perovskite has been used as a model for investigating the relative importance of the Jahn‐Teller (JT) lift of degeneracy, the ScF 6 octahedra rotation (OR), and the quadrupole‐quadrupole interaction linked to different occupancy of the Sc t 2g subshell in various sites of the unit cell (orbital ordering, OO). The group‐subgroup sequence Pm3¯m, P4mmm, P4mbm, and Pnma, supplemented by Cmmm and I4mcm, has been explored by using an all electron Gaussian type basis set, hybrid functionals, and the CRYSTAL17 code. The JT lift of degeneracy provides a stabilization about 5 times larger than the sum of the OO and OR effects. The energy gained in the transition from P4mmm to P4mbm, consisting in a rotation of the octahedra around the c axis, is 1077 μE h. From P4mbm to Pnma, additional rotations around the a and b axes are possible, and the d Sc electron can occupy a different t 2g orbital, with a total energy reduction of 2318 μE h. The rotation of the octahedra reduces the strength of superexchange: in going from P4mmm to Pnma the G‐AFM stabilization with respect to FM shrinks by a factor 4. [ABSTRACT FROM AUTHOR]