Symmetry breaking tranforms strong to normal correlation and false metals to true insulators
ORAL
Abstract
Band theory based on mean-field-like approaches such as density functional theory (DFT) is known to incorrectly predict metallic character for insulating transition-metal oxides. Such failure in many cases that was not fixed by advanced DFT exchange-correlation functionals, has been the historic reason behind introducing strong correlation methodologies while retaining a highly symmetric structural framework for such compounds. Allowing, however, energy-lowering symmetry breaking such as cation dimerization, Jahn-Teller distortion, dipolar configurations, and local magnetic configurations fixes the gap problem, selectively predicting insulating states when observed (LaTiO3, VO2, Nb3Cl8, etc.), yet predicting metallic states when observed (SrVO3) without the intervention of strong correlations. This approach distinguishes between paramagnetic phases that are insulators and those that are metals and shows band narrowing and mass enhancement in Mott metals. High symmetry can produce degeneracy that calls for strong correlation to disentangle. Symmetry breaking reduces such degeneracies, thus transforming strong correlation to normal correlation that a density functional approximation can describe. Examples are discussed, including successful treatment of gapping in ordered magnetic systems and short-range ordered paramagnetic or paraelectric phases. This is not a replacement of correlation theory but explains when strong correlation is not the required solution.
*The work of AZ was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division, under Grant No. DESC0010467. The work of JPP was supported by the National Science Foundation under Grant No. DMR-2426275, and by the Department of Energy, Office of Science, Basic Energy Sciences, under Grant No. DE-SC0018331.
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Publication:[1] Jia-Xin Xiong, Xiuwen Zhang, and Alex Zunger, Symmetry breaking forms split-off flat bands in quantum oxides controlling metal versus insulator phases, Phys. Rev. B 111, 035154 (2025). [2] Jia-Xin Xiong, Xiuwen Zhang, and Alex Zunger, Role of magnetic and structural symmetry breaking in forming the Mott insulating gap in Nb3Cl8, Phys. Rev. B 111, 155122 (2025). [4] Xiuwen Zhang, Jia-Xin Xiong, and Alex Zunger, Hidden magnetism and split off flat bands in the insulator metal transition in VO2, npj Comput. Mater. 10, 217 (2024). [5] John P. Perdew, Adrienn Ruzsinszky, Jianwei Sun, Niraj K. Nepal, and Aaron D. Kaplan, Interpretations of ground-state symmetry breaking and strong correlation in wavefunction and density functional theories, Proc. Natl. Acad. Sci. 118, e2017850118 (2021). [6] Alex Zunger, John P. Perdew, and Jia-Xin Xiong, Symmetry breaking transforms strong to normal correlation and false metals to true insulators, In process.
