$\alpha \text{−}{\mathrm{MnO}}_2$ is an emerging material for electronic, optoelectronic, and energy applications, owing to its structural flexibility and defect-driven functionality. During synthesis of $\alpha \text{−}{\mathrm{MnO}}_2$, native oxygen vacancies readily form and are typically compensated by foreign dopants. A thorough understanding of intrinsic defects is therefore essential for enabling controlled extrinsic doping and optimizing material performance. Using a density functional approach, we investigate the structural, electronic, magnetic, and optical properties of the ground-state C2-type antiferromagnetic $\alpha \text{−}{\mathrm{MnO}}_2$ in the presence of native point defects, including interstitials, vacancies, and antisites. We compute their thermodynamic stability, incorporating electrostatic corrections to eliminate spurious long-range interactions. Mn interstitial $\left({\mathrm{Mn}}_{\text{i}}\right)$ and Mn antisite on an O site $\left({\mathrm{Mn}}_{\text{O}}\right)$ introduce shallow donor levels, whereas O vacancy $\left({\mathrm{V}}_{\text{O}}\right)$ exhibits amphoteric behavior and acts as compensating centers. The calculated defect formation energies reveal pronounced competition between donor- and acceptor-type native defects, leading to strong intrinsic defect compensation under both Mn-rich and O-rich growth conditions. The presence of defects significantly perturbs the electronic structure of $\alpha \text{−}{\mathrm{MnO}}_2$, introducing spin-polarized midgap states, while O interstitial $\left({\mathrm{O}}_{\text{i}}\right)$ preserves the host antiferromagnetic order. Mn vacancy $\left({\mathrm{V}}_{\text{Mn}}\right)$ remains ionized across the band gap and behaves as a shallow acceptor, suggesting its potential role under suitable nonequilibrium growth conditions, whereas O antisite on a Mn site $\left({\mathrm{O}}_{\text{Mn}}\right)$ forms deep acceptor levels. $\mathrm{BSE}@G_0{W}_0$ calculations reveal a strongly anisotropic optical response in stoichiometric $\alpha \text{−}{\mathrm{MnO}}_2$, while native point defects introduce pronounced sub-gap excitations and enhanced dielectric screening, with vacancies producing the largest effect.

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• Electronic structure
• First-principles calculations
• Point defects
• Transition metal oxides