In his seminal work, N. Mott theorized that the insulating behavior of 3d transition metal oxides emerges from the strong correlation, encoded by the on-site inter-electronic repulsion (“U”) between d electrons. This repulsion keeps the d electrons localized within bands of width W where U>W , and was argued as the correct mechanism regardless of the magnetic order. This picture of doubly-occupied and empty bands is the text book model of (Mott) insulation. At the same time, it created a general position in the literature that mean-field like single determinant approaches such as DFT are inappropriate for describing the broad science issues of 3d oxides, such as catalysis, thermoelectric, photovoltaics, etc. The highly correlated approach builds upon the observation that DFT is inappropriate because it can not explain paramagnetism as a non magnetic state. We explored the alternative option of staying within (single determinant) mean field DFT but getting rid of Naive -DFT approximations by allowing spontaneous symmetry breaking if it lowers the total energy . This generalization creates finite band gaps in AFM and PM phases of ABO3 perovskites (except PM SrVO3 and CaVO3 that are metals), disproportionation (in SmNiO3 and YNiO3), mass enhancement (in SrVO3 and doped SrTiO3) and explains the observed trends in JT distortions throughout the series.
Recent relevant references:
J. Varignon, M. Bibes and Alex Zunger, "Origin of band gaps in 3d perovskite oxides“ Nature Commun., 10, 1658 (2019).
Alex Zunger, "Beware of plausible predictions of fantasy materials" Nature 566, 447-449 (2019)
Julien Varignon, Manuel Bibes, and Alex Zunger, "Mott gapping in 3d ABO3 perovskites without Mott-Hubbard interelectronic repulsion energy U“ Phys. Rev. B 100, 035119 (2019).
Qihang Liu, Gustavo M. Dalpian and Alex Zunger, "Anti-doping in Insulators and Semiconductors Having Intermediate Bands with Trapped Carriers“ Physical Review Lett. 122, 106403
Qihang Liu, Qiushi Yao, Z. A. Kelly, C. M. Pasco, T. M. McQueen, S. Lany, Alex Zunger "Electron Doping of Proposed Kagome Quantum Spin Liquid Produces Localized States in the Band Gap" Physical Review Letters. 121, 186402 (2018)
G. M. Dalpian, Q. Liu, J. Varignon, M. Bibes, and Alex Zunger, "Bond disproportionation, charge self-regulation, and ligand holes in s-p and in d-electron ABX3 perovskites by density functional theory" Phys. Rev. B 98, 075135 (2018).
Julien Varignon and Manuel Bibes and Alex Zunger Origins Vs. fingerprints of the Jahn-Teller effect in d-electron ABX3 perovskites” Phys. Rev. Research (In Press)
O. I. Malyi, G. M. Dalpian, X. Zhao, Zhi Wang, and Alex Zunger "Realization of predicted exotic materials: The burden of proof“ Materials Today (In Press, 2019)