Transition metal perovskite oxides ABO3 have a very rich array of properties, and many compounds show an insulating behavior, despite the presence of a finite number of d electrons. This insulating character is often ascribed to dynamical electron correlations, but perovskites also possess structural distorsions that break symmetries, lift electronic degeneracies, and may thus also open band gaps. In a paper just published in Nature Communications, we show that if one allows symmetry-breaking energy-lowering crystal symmetry reductions and electronic instabilities within Density Functional Theory (DFT), one successfully and systematically recovers the trends in the observed band gaps, magnetic moments, type of magnetic and crystallographic ground state, bond disproportionation and ligand hole effects, Mott vs. charge transfer insulator behaviors, and the amplitude of structural deformation modes including Jahn-Teller in low temperature spin-ordered and high temperature disordered paramagnetic phases. Since DFT does not include dynamic correlations, our work suggests that they do not play a major role in determining the metallic or insulating nature of these oxides. In other words, ABO3 may be complicated, but they are not necessarily strongly correlated.
This work was performed in collaboration with the University of Colorado at Boulder.
Origin of band gaps in 3d perovskite oxides
Julien Varignon, Manuel Bibes & Alex Zunger, Nature Commun. 10, 1658 (2019)