On the role of the exact Hartree-Fock exchange in determining the Jahn-Teller energy splitting and electronic band gap in the KBF₃ (B=Sc, Ti, Fe, Co, Cr and Cu) perovskites. A quantum mechanical investigation

KBF3 perovskites present a partially filled t(2g) (Sc, Ti, Fe or Co), or e(g) (Cr or Cu) subshell. The role of the adopted functional on the Jahn-Teller (JT) splitting, band gap, and cell deformation is investigated. Results obtained with PBE, HSE06, B3LYP, PBE0, Hartree-Fock and a new functional PBE(X), in which X is the percentage of HF exchange (0 to 100%) are compared, revealing that the JT splitting and energy gap depend dramatically on X, while the correlation and local exchange terms composing the functionals have a slight influence on the investigated properties.