Structure and electron affinity of (1120)-X 4H-SiC surface

•Terminated SiC (1120) surface is investigated for structure and surface electronic properties.•All adsorbates react exothermically with the unterminated SiC surface.•Cl and F termination results in a range of large positive electron affinities (3.9 and 5.1 eV).•H and Li termination decrease the electron affinity (1.9 and 0.1 eV).•Particular emphasis is put on lithium reducing the electron affinity (EA) to near zero.•EA plays a crucial role in the efficiency and performance surface applications, namely emission.