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Density functional theory calculations were performed on $\text{SmNiO}_3/\text{BaTiO}_3$ superlattices to investigate electronic reconstruction mechanisms at correlated ferroelectric heterointerfaces. The study reveals that polar discontinuities are fully compensated through a spatial reorganization of the intrinsic Ni charge disproportionation—transferring 1 $e$/f.u. across the slab to establish uniform $\text{Ni}^{2+}$ and $\text{Ni}^{4+}$ monolayers at opposing terminations instead of triggering conventional ionic defects or carrier doping. This identifies charge disproportionation rearrangement as an intrinsic screening mechanism across complex transition-metal oxides, with formal analysis of $\text{BiNiO}_3$ showing that stronger polar discontinuities drive even more complex interfacial charge orderings.
Correlated nickelate interfaces can completely screen massive ferroelectric polar discontinuities without structural defects or free carriers, relying instead on a clean spatial reshuffling of their local $\text{Ni}^{2+}/\text{Ni}^{4+}$ disproportionation patterns.
We use density functional theory (DFT) to demonstrate rearrangement of charge disproportionation as a new mechanism for screening polar discontinuities at heterointerfaces. We focus on SmNiO$_3$, a III-III perovskite characterized by an insulating ground state that originates from disproportionation of the electrons at the Ni sites. When interfaced with ferroelectric, II-IV perovskite BaTiO$_3$, this system can display a polar discontinuity whose magnitude is determined by the nature of the interface (NiO$_2$-BaO or SmO-TiO$_2$) and the orientation of the BaTiO$_3$ spontaneous polarization. In the orientation maximizing the interface charge, SmNiO$_3$ compensates by transferring 1 $e$/f.u. between the two interfaces and modifying the disproportionation sequence from Ni$^{4+}$/Ni$^{2+}$ to Ni$^{2+}$/Ni$^{2+}$ at the SmO-TiO$_2$ interface and to Ni$^{4+}$/Ni$^{4+}$ at the NiO$_2$-BaO interface. While this mechanism is potentially universal in all perovskites exhibiting charge disproportionation, our formal analysis of BiNiO$_3$/BaTiO$_3$ superlattices suggests that larger polar discontinuities may need more complex disproportionation patterns for screening.