The charge and spin density of five LaBO3 perovskites (B=Sc, Ti, V, Cr and Co). A Mulliken analysis

Abstract

The charge and spin density distributions of five LaBO${}_3$ perovskites (B = Sc, Ti, V, Cr, and Co) have been investigated through the Mulliken population analysis, which yields crucial insights into the net atomic charges Q, magnetic moments $\mu$, and bond populations BP. The occupancy of the d shell and of the individual d orbitals of the transition metals B are also discussed. Large differences are observed with respect to the fully ionic representation (or oxidation state), La${}^{+3}$, B${}^{+3}$ and O⁻², which implies that the B atom loses the two 4s electrons and one of the d electrons, so that Sc would be d${}^0$, Ti d${}^1$, V d${}^2$ and so on. The results of the quantum mechanical calculations (with an all electron Gaussian type basis set, hybrid functionals and the CRYSTAL code) show that the d occupancy on B is very close to the one of the isolated neutral atom: Sc=0.91 vs 1.0, Ti=2.02 vs 2.0, V=2.91 vs 3.0, Cr=4.07 vs 4.0, Co 7.07 vs 7.0, in contrast with the fully ionic model. The net atomic charges, Q, on the atom B, are far from the ionic limit: +2.06, +1.92, +2.05, +1.81 and +1.74 from Sc to Co. The B net charges are then close to +2(instead of the formal ionic value of +3), with a maximum difference of −0.3 for Co. This lower atomic charge is compensated by the oxygen charge which is slightly oscillating between −1.48 and −1.62 (instead of −2), whereas the La net charge is around +2.70 (instead of the formal +3 value). The reduced ionicity involves then, rather than the d shell, the partial occupancy of the 4s orbitals and their interaction with the p orbitals of oxygen. At variance with respect to Q, the atomic magnetic moments $\mu$ are very close to the ideal values: 0.96 vs 1 $\left|e\right|$ for Ti, 1.90 vs 2 $\left|e\right|$ for V, 2.88 vs 3 $\left|e\right|$ for Cr (the ground state of the Sc and Co compounds is closed shell, with no spin polarization). The Q and $\mu$ values of three fluorides (KScF${}_3$, KCrF${}_3$, KCoF${}_3$) are also presented, to evidentiate the large differences between oxides and fluorides.