Electronic structure of the layer compounds GaSe and InSe in a tight-binding approach

The three-dimensional band structure of the III-VI layer compounds GaSe and InSe has been investigated in the tight-binding approach. The pseudo-Hamiltonian matrix elements in the sp^3s^* basis are fit in order to reproduce the nonlocal pseudopotential band structure, in the framework of constrained optimization techniques using the conjugate gradient method. The results are in good agreement with the optical and photoemission experimental data. The scaling laws appropriate to the covalent bonding are violated by a fraction of eV only, which suggests that the interlayer interactions are not solely of the van der Waals type.