Electronic-transport calculations were performed using the AMSET code. Uniform band-structure calculations were performed using the HSE06 hybrid functional and expanded 8 × 8 × 12 k-point meshes to obtain accurate bandgaps E g and sets of Kohn-Sham wavefunction coefficients. (We note that PBEsol predicts a metallic electronic structure for Bi 2 TeO 2 .) These meshes were increased by a factor of 20 using interpolation for the transport calculations. Electron relaxation times were calculated by summing scattering rates from three different processes, viz. acoustic deformation potential (ADP), polar optical phonon (POP) and ionised impurity (IMP) scattering. Deformation potentials were computed by performing a series of singlepoint electronic-structure calculations on deformed structures generated using AMSET. For these calculations, the HSE06 functional was used with the "base" k-point meshes used for the geometry optimisations. Elastic constants were computed using PBEsol and the finite-differences routines in VASP. High-frequency and static dielectric constants ε ∞ and ε s = ε ∞ +ε ionic were determined using the linear-optics and finite-difference routines in VASP, respectively. . The ε ∞ was determined using the "base" 4 × 4 × 6 k-point mesh with the HSE06 functional, while the ionic contribution was determined using an expanded 8 × 8 × 12 mesh with PBEsol. The POP frequencies ω po were determined from the phonon frequencies at q = Γ, obtained using Phonopy, and the infrared (IR) activities determined using the Phonopy-Spectoscopy package and Born effectivecharge tensors Z * from density-functional perturbation theory (DFPT) calculations with PBEsol. (We note that the fourth scattering mechanism modelled by AMSET, piezoelectric (PIE) scattering, is not relevant to Bi 2 ChO 2 since the piezoelectric moduli vanish by symmetry in the centrosymmetric I4/mmm spacegroup.)