Theoretical studies on the structural, electronic, and optical properties of Ag ₂HgSnSe ₄

We investigate the electronic structure of Ag ₂HgSnSe ₄ in a wurtzite - stannite structure with the first principles method. This crystal is a direct band-gap compound. In addition the dielectric function, absorption coefficient, reflectivity, and energy-loss function are studied using the density functional theory in the generalized gradient approximation. We discuss the optical transitions between the valence bands and the conduction bands in the spectrum of the imaginary part of the dielectric function at length. We also find a very high absorption coefficient and a wide absorption band for this material. The prominent structures in the spectra of reflectivity and the energy-loss function are discussed in detail.