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

Abstract

The geometrical, electronic and vibrational properties of LaCrO${}_3$ have been investigated by using an all electron Gaussian type basis set, the B3LYP functional and the CRYSTAL code, and compared with KVF${}_3$: in the two compounds the transition metal is formally in d${}^3$ configuration. The high spin t${}_{2g}^3$ 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$\overline{3}\text{m}$, N. 221, to space group $P\frac{4}{m}\mathrm{bm}$, N.127, and to $I\frac{4}{m}\mathrm{cm}$, N. 140) in the oxide is about 70 times larger than in the fluoride (5.4 vs. 0.08 mE${}_h$), 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${}_3$, 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.