Symmetry-Breaking Polymorphous Descriptions for Correlated Materials without Interelectronic <i>U</i>

Correlated materials with open-shell d- and f-ions having degenerate band edge states show a rich variety of interesting properties. The textbook view for the electronic structure of these materials is that mean-field approaches are inappropriate, as the interelectronic interaction U is required to open a band gap between the occupied and unoccupied degenerate states while retaining symmetry. We show that the mean-field band theory can lift such degeneracies when nontrivial unit cell representations (polymorphous networks) are allowed to break symmetry, in conjunction with a recently developed non-empirical exchange and correlation density functional without an on-site interelectronic interaction U. We rationalize how density functional theory (DFT) in the polymorphous representation achieves band gap opening in correlated materials through a separate mechanism to the Mott-Hubbard approach. We show the method predicts magnetic moments and gaps for four classical 3d transition-metal monoxides in both the antiferromagnetic and paramagnetic phases, offering a highly-efficient alternative to symmetry-conserving approaches for studying a range of functionalities in open d- and f-shell complex materials.