The Infrared and Raman Spectra of the Jahn–Teller‐Distorted KCrF 3 Perovskite

The IR and Raman spectra of the KCrF 3 perovskite are evaluated by imposing the monoclinic I112/m space group, experimentally stable at low temperature, and the tetragonal I4/mcm space group, observed above 150 K. The B3LYP total energy difference Δ E between the two phases is very small: 0.2 mE h (about 0.06 eV) per formula unit. The differences in the spectra for the two space groups are analyzed, as well as the FM to AFM modifications. In spite of the large deformation of the CrF 6 octahedron (the three Cr‐F distances are 2.01 and 2.36 Å in the ab plane, and 2.05 Å along c in the monoclinic low‐temperature structure), the spectra obtained with the two space groups are very similar and remind one of the ideal reference cubic spectra, characterized by only three IR‐active peaks and no signal for Raman. Calculations are performed at the quantum mechanical level by using an all‐electron Gaussian‐type basis set and the full‐range hybrid B3LYP functional.