ELECTRONIC-STRUCTURE OF SNS2, SNSE2, CDI2 AND PBI2

The band structures of the layer compounds SnS2, SnSe 2, CdI2 and PbI2 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 L1+ indirect gap and a main optical transition due to anion p-cation p orbitals is found, whilst for PbI2 the gap is direct at A.