First-principles DFT + U studies of the atomic, electronic, and magnetic structure of α-MnO2 (cryptomelane)

► The octahedral molecular sieve material α-MnO2 is studied via density functional theory. ► As little as 0.002 K+ per MnO2 formula unit stabilizes α-MnO2 over β-MnO2. ► α-MnO2 is predicted to be an antiferromagnetic, 1.3 eV bandgap, semiconductor. ► α-MnO2 readily accepts water and related oxygen hydrides. ► Inside α-MnO2, the equilibrium K-HxO distance increases with increasing x.