Moving to a higher carrier concentration of 1 × 10 20 cm -3 (Figure ), the effects of both POP and PIE scattering are diminished further, while ionised impurities begin to control the charge transport behaviour in CuI -a room temperature hole mobility of 32.6 cm 2 V -1 s -1 is predicted. IMP (and indeed POP scattering in the AMSET implementation) scattering is largely determined by the value of the static dielectric response of a material, i.e. its ability to screen electric charge. For CuI, calculated dielectric constants range from 5.27 to 8.85, dependent on the flavour of DFT functional and the method used to calculate the high-and low-frequency responses, and are shown in Table . Meanwhile, an experimental dielectric response of 6.5 is reported by Hanson et al. Accurate calculation of the dielectric response in tetrahedral semiconductors is benchmarked by Skelton et al., who note that semi-local DFT nearly always overestimates the high-frequency dielectric response, while hybrid functionals nearly always underestimate the high-frequency dielectric response, with PBE0 performing worse than HSE06. Considering the tetrahedral zincblende structure of CuI, it is reasonable to assume that similar trends are followed here. Due to the fact that the dielectric constant is quite small for CuI, these quite large percentage errors in 𝜖 0 have significant effects on the POP and IMP scattering rates, as shown in Figure in the Supplementary Information. To this end, the dielectric constant used in the AMSET calculations in Figures and is that determined from experiment (6.5, where 𝜖 ionic is set as the calculated value of 1.1 from DFPT, and the remainder is assigned to 𝜖 ∞ ), with lower and upper limits (5.27 and 8.85) shown for context in the SI. More sophisticated methods for calculating the dielectric response that can accurately model excited state features, such as GW (Green's function 𝐺 with screened Coulomb interaction 𝑊 ) and BSE (Bethe-Salpeter equation) implementations, would provide a clearer picture, but exceed the scope of the current work. --6.5