The calculated electronic band structures and density of states (DoS) curves of Pnma and R3m GeSe are presented in Fig. , and those of GeS are presented in Fig. ). For both Pnma phases the conduction band minima (CBM) and valence band maxima (VBM) lie at different points along the Γ → X direction, resulting in indirect bandgaps of E g = 1.32 and 1.17 eV respectively. The CBM and VBM of the two R3m phases are both located at the k k k = L wavevector, as in the rocksalt Pb and Sn chalcogenides, resulting in a direct gap of E g = 0.3 eV. These predictions are generally in very good agreement with experimental measurements and previous calculations. We note, however, that previous computational studies on R3m GeS and GeSe predicted much larger E g , which we attribute to insufficiently dense k k k-point meshes (cf. Table and Fig. , ESI † ). The calculated bandgaps of Pnma GeS and GeSe are larger than the 0.93 and 0.82 eV predicted for Pnma SnS and SnSe in our previous work. On the other hand, the E g of the R3m phases are considerably smaller than the 0.6 eV we predicted for rocksalt SnS and SnSe, which suggests the rhombohedral distortion in GeS and GeSe may lead to a significant narrowing of the gap.