Electronic-structure calculations were performed using the HSE06 hybrid functional to obtain accurate electronic bandgaps E g and were used as the basis to model the electronic transport properties using the AMSET code. Uniform band structures were calculated with PBEsol+D3 and k k k-point meshes with two times the number of subdivisions along each reciprocal lattice vector as those used for the geometry optimisations (2.5× for R3m GeS), and a scissors operator applied to increase the E g to the HSE06 values. Four scattering mechanisms were considered to determine the electronic relaxation times, viz. acoustic deformation potential (ADP), piezoelectric (PIE), polar optical phonon (POP), and ionized impurity (IMP) scattering. The high-frequency dielectric constants ε ε ε ∞ were ob-tained as the real part of the energy-dependent dielectric function