  In some d-electron oxides the measured effective mass m(exptl) has long been
known to be significantly larger than the model effective mass m(model) deduced
from mean-field band theory, i.e., m(exptl) = beta * m(model), where beta > 1
is the "mass enhancement", or "mass renormalization" factor. Previous
applications of density functional theory (DFT), based on the smallest number
of possible magnetic, orbital, and structural degrees of freedom, missed such
mass enhancement, a fact that was taken as evidence of strong electronic
correlation being the exclusive enabling physics. The current paper reports
that known modalities of energy-lowering symmetry-broken spin and structural
effects included in mean-field DFT show mass enhancement for both electrons and
holes in a range of d-electron perovskites SrVO3, SrTiO3, BaTiO3, and LaMnO3 as
well as p-electron perovskites CsPbI3 and SrBiO3, including metals (SrVO3) and
insulators (the rest). This is revealed only when enlarged unit cells of the
same parent global symmetry, which are large enough to allow for symmetry
breaking distortions and concomitant variations in spin order, are explored for
their ability to lower the total energy. The paper analyzes the contributions
of different symmetry-broken modalities to mass enhancement, finds common
effects in the range of d- as well as p-electron perovskites. Thus, symmetry
breaking in mean-field theory could describe effects that were previously
attributed exclusively to complex correlated treatments. Indeed, broken
symmetries are often experimentally observed, e.g., octahedral tilting,
Jahn-Teller distortions, or bond disproportionation, and often provide
intuitive explanations in terms of degeneracy removal due to lowering of
structural symmetry, or as shifting of band energies in explainable directions.
