  Reversible intercalation of hydrogen into samarium nickelate, SmNiO$_3$
(SNO), has been of recent interest. Upon entering SNO, the hydrogen
dissociates: the H$^+$ binds to an oxygen and the valence electron localizes on
a nearby NiO$_6$ octahedron, resulting in a local dipole moment. In this work,
we use first-principles calculations to explore the polar states of
hydrogen-doped SNO at a concentration of 1/4 hydrogen per Ni. The inherent tilt
pattern of SNO and the presence of the interstitial hydrogen present an
insurmountable energy barrier to switch these polar states to their
symmetry-related states under inversion. We find a sufficiently low barrier to
move the localized electron to a neighboring NiO$_6$ octahedron, a state
unrelated by symmetry but equal in energy under epitaxial strain, resulting in
a large change in polarization. We term this unconventional ferroelectric a
"fraternal-twin" ferroelectric.
