Fe-Induced Electronic Modulation In α-MnO₂: A DFT + U Study for Advanced Cathode Materials

Abstract

The α-phase of manganese dioxide (MnO 2 ) attracts significant attention because its hollandite tunnel framework enables effective ion storage and maintains structural resilience. The electronic properties of α-MnO 2 , especially its band gap and key orbitals, play a crucial role in determining its electrochemical behavior. We use DFT+U calculations with the Quantum ESPRESSO package, applying the PBE functional and Hubbard correction for Mn 3d orbitals, to examine the impact of Fe substitution on the electronic and structural properties of α-MnO 2 . With a valence band maximum of O 2p and a conduction band minimum of Mn 3d character, exhibiting significant hybridization, Pristine α-MnO 2 is verified as an indirect band gap semiconductor (Eg = 1.08 eV). Upon Fe doping, the electronic structure is significantly modified, showing band gap narrowing and a transition toward metallic behavior under partial oxidation. PDOS analysis reveals dopant-induced states at the Fermi level. HOMO and LUMO isosurface visualizations using VESTA show localized charge redistribution and Mn–O hybridization. Structural analysis confirms preservation of the tunnel architecture with minor distortions and no secondary phase formation. Doping with iron allows the adjustment of electronic conductivity without compromising the material’s structural framework, enhancing FeMnO 2 ’s potential for lithium- and sodium-ion battery cathodes.