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Recent experimental work has realized a new insulating state of samarium nickelate $({\mathrm{SmNiO}}_{3})$, accessible in a reversible manner via high-density electron doping. To elucidate this behavior, we use the first-principles density functional theory $(\mathrm{DFT})+U$ method to study the effect of added electrons on the crystal and electronic structure of ${\mathrm{SmNiO}}_{3}$. First, we track the changes in the crystal and electronic structure with added electrons compensated by a uniform positive background charge at concentrations of $\frac{1}{4}$, $\frac{1}{2}$, $\frac{3}{4}$, and 1 electrons per Ni. The change in electron concentration does not rigidly shift the Fermi energy; rather, the added electrons localize on ${\mathrm{NiO}}_{6}$ octahedra causing an on-site Mott transition and a change in the density of states resulting in a large gap between the occupied and unoccupied Ni ${e}_{g}$ orbitals at full doping. This evolution of the density of states is essentially unchanged when the added electrons are introduced by doping with interstitial H or Li ions.