Investigation of electrical and linear optical properties under pressure SnS, SnSe and GeS compounds

In this thesis, the lattice parameters, atomic positions, electronic energy band structure, density of states (DOS) and optical properties of SnS, SnSe ve GeS compounds in the orthorhombic phase were investigated by using density functional theory (DFT) within the local density approximation (LDA) for exchange-correlation under pressure. The quasipartice band structures for these compounds are computed with G0W0 approximation for the exchange-correlation self-energy. The band structure shows an indirect band gap 0.644 eV (SnS) at (Γ-Z→Γ-Y) point, 0.503 eV (SnSe) at (Γ-Y→ Γ-Y) point, and 1,027 eV (GeS) at (Γ-Z→ Γ) point in the Brillouin zone at ambient pressure. We have also determined the real and imaginary part of the dielectric function as a function of the energy in the range 0-30 eV using G0W0 + Independent Particle Approximation (IPA) under pressure. Some optical constants such as the absorption coefficient, energy-loss function, refractive index, reflectivity, and extinction coefficient were computed from the real and imaginary part of the dielectric function. The obtained results were compared with the available experimental and theoretical values.