The Structural, Electronic and Vibrational Properties of LaCrO 3 $$ {}_3 $$ . A Quantum Mechanical Investigation by Using an All Electron Gaussian Type Basis Set and a Full Range Hybrid Functional.

The geometrical, electronic and vibrational properties of LaCrO 3 $$ {}_3 $$ have been investigated by using an all electron Gaussian type basis set, the B3LYP functional and the CRYSTAL code, and compared with KVF 3 $$ {}_3 $$ : in the two compounds the transition metal is formally in d 3 $$ {}^3 $$ configuration. The high spin t 2 g 3 $$ {}_{2g}^3 $$ ground state excludes the Jahn Teller deformation and the orbital ordering. The energy gain due to the rotation of the octahedra (from the cubic space group Pm 3 ¯ m $$ \overline{3}\mathrm{m} $$ , N. 221, to space group P 4 m bm $$ P\frac{4}{m} bm $$ , N.127, and to I 4 m cm $$ I\frac{4}{m} cm $$ , N. 140) in the oxide is about 70 times larger than in the fluoride (5.4 vs. 0.08 mE h $$ {}_h $$ ), due to the larger electrostatic forces (a factor four, as the formal charge doubles in going from F- to O2-) and the consequently reduced B-X distances. In KVF 3 $$ {}_3 $$ , the p states of fluorine are separated by 6.4 eV from the d states of vanadium, whose band is quite narrow (1 eV). In the oxide, on the contrary, the oxygen p states overlap to a large amount with the d states of chromium, whose band is more than 6 eV large. The FM and AFM energy differences, the spin density maps and profiles, and the Mulliken analysis data are also provided for documenting the differences between the oxide and the fluoride.