view and editing, supervision, project administration, funding acquisition. DOS: conceptualisation, resources, writing -review and editing, supervision, project administration, funding acquisition. values (and convergence of these parameters) can found in the Supplementary Information. A dense uniform Γ-centred k-point mesh of 14 × 14 × 14 was used to obtain the wavefunction overlaps for determining scattering rates, and the corresponding band structure was plotted using the SUMO package. The deformation potentials were calculated from density of states calculations using the same convergence parameters as bulk calculations. The low-frequency dielectric constant, piezoelectric constant and polar optical phonon frequency were calculated using both density functional perturbation theory (DFPT) and finite differences (FD) implementations in VASP. The high-frequency dielectric constant was calculated with the PBE0 functional using the independent particle random phase approximation (IP-RPA) optics routine in VASP and converged against the number of empty bands and k-point density.