Design principles for the discovery of non-cubic polymorphous networks*

Symmetry breaking resulting in the formation of a distribution of local structural and/or spin motifs (i.e., polymorphous network) has been experimentally observed and theoretically described for a number of cubic ABX₃ perovskites (e.g., CsPbI₃, CsSnI₃, BaTiO₃, and PbTiO₃), demonstrating that properties of such compounds cannot be predicted accurately with density functional theory (DFT) using high-symmetry Pm-3m monomorphous unit cells. Herein, we show that structural and/or spin symmetry breaking is not limited to cubic ABX3 systems but exists for a range of paraelastic, paraelectric, and paramagnetic non-cubic compounds (e.g., GeTe, Bi₂O₃, EuTiO₃, and YNiO₃). Importantly, such potential polymorphous compounds can be predicted successfully based on the analysis of group/subgroup crystal symmetries and their relative energetics. Using such group/subgroup relations and DFT, we form an extensive list of realistic symmetry-broken polymorphous compounds ready for experimental validation. We also demonstrate that accounting for symmetry breaking can allow describing correctly the electronic structure of potential polymorphous compounds without including any dynamic correlation.