Electronic and optical properties of GaS: A firstprinciples study

The electronic band structure and optical properties of hexagonal GaS are investigated using the density functional theory. The calculated band structure shows that the crystal has an indirect band gap with the value of 1.54 eV in the Brillouin zone at the Γ-M. The structural optimization has been performed using the generalized gradient approximation (GGA) and the local density approximation (LDA). The calculated structure optimization of GaS has been compared with the experimental results and has been found to be in good agreement with each other. Furthermore, the linear photon-energy-dependent dielectric functions and some optical constants such as energy-loss functions for volume and surface, extinction, reflectivity and absorption coefficients, refractive index and effective number of valence electrons per unit cell participating in the interband transitions have been calculated.?