Electronic structure of SnS2, SnSe2, CdI2and PbI2

The band structures of the layer compounds SnS 2 , SnSe 2 , CdI 2 and PbI 2 are calculated by the tight-binding method. They are in closer agreement with experimental results and previous pseudopotential calculations than previous tight-binding results have been. A universal band structure for the family is found by use of approximate algebraic band energies. For the 16-electron crystals a Gamma 2 - to L 1 + indirect gap and a main optical transition due to anion p-cation p orbitals is found, whilst for PbI 2 the gap is direct at A.