Electronic structure of arsenic chalcogenides

A nonempirical localized-orbital approach is used to calculate the electronic structure of As₂{S}₃$, ${As}₄S₄, As₂{Se}₃$, ${As}₄Se₄, and As₂{Te}₃$ crystals. Contributions of $s$, $p{σ}$, and $p$ lone-pair orbitals to the various molecular levels are illustrated. Densities of occupied states agree closely with experimental photoemission data. The fundamental absorption edges in ${As}₂S₃ and As₂{Se}₃$ are found to correspond to indirect gaps, but with several other indirect and direct transitions within a few tenths of an eV of the indirect edge, consistent with most of the optical-absorption studies. The method is readily applicable to the electronic structure of fully coordinated random networks but because of the severe self-consistency problems we are unable to tackle problems associated with thermal relaxation at wrongly coordinated atoms.