Topological States in β-PbO₂?

The electronic properties of β-PbO₂, have been controversial for over a century. Experiments find metallic behavior, attributed to its defect structure, to indirect semiconducting for stochiometric samples, with a gap of 0.61 eV. Theory leads to similar ambiguities, and predicts this phase to be metallic (PBE, HSE06) or the opening of too small a bandgap (HSE06). An area where this inconsistency is significant, is when a material property depends on the electronic structure in the vicinity of the Fermi energy, such as topological states. In our work, we use a self-consistent DFT+U approach and find stochiometric β-PbO₂ to be an indirect semiconductor with a band gap of ~0.8 eV, similar to experiment. The larger bandgap requires strains of ~4% to drive β-PbO₂ into a nodal line semimetallic state, which is not protected under the application of spin-orbit-coupling. Moreover, our surface computations do not show any topologically protected states near the Fermi energy. Therefore, our results show that in contrast to previous computations β-PbO₂ is a topologically trivial material, consistent with experiment. Differences to previous work can be attributed to our more accurate description of the optical properties of bulk β-PbO₂.