Using first-principles density functional theory we predict a ferroelectric
ground state -- driven by off-centering of the magnetic Mn4+ ion -- in
perovskite-structure BaMnO3​.
Our finding is surprising, since the competition between energy-lowering
covalent bond formation, and energy-raising
Coulombic repulsions usually only favors off-centering on the perovskite
B-site for non-magnetic d0 ions.
We explain this tendency for ferroelectric off-centering by analyzing the
changes in electronic structure between the centrosymmetric and polar states,
and by calculating the Born effective charges; we find anomalously large values
for Mn and O consistent with our calculated polarization of 12.8 μC/cm2.
Finally, we suggest possible routes by which the perovskite phase may be
stabilized over the usual hexagonal phase, to enable a practical realization of
a single-phase multiferroic.Comment: 6 pages, 3 figure