Étude ab initio des propriétés structurales, électroniques et optiques du BeSe dans les phases zinc blende et NiAs

Abstract

This thesis presents an ab initio study of the structural, electronic and optical properties of beryllium selenide (BeSe) in the Zinc Blende and NiAs phases, carried out using density functional theory (DFT) with the GGA-PBE approximation, as implemented in the CASTEP code. Structural optimization showed that the Zinc Blende phase is the most stable under ambient pressure, with lattice parameters and a bulk modulus (B₀ ≈ 92 GPa) in good agreement with the literature, while a phase transition to the NiAs structure occurs under high pressure (≈ 55 GPa). The electronic study reveals semiconducting behavior in both phases, with an indirect Γ→X band gap of 2.74 eV for Zinc Blende and 0.60 eV for NiAs, with valence bands dominated by Se-4p orbitals and conduction bands by Be-2s/Se-p orbitals, reflecting covalent hybridization. Optical analysis (absorption, reflectivity, refractive index, dielectric function, loss function and optical conductivity) highlights strong activity in the ultraviolet region, confirming the potential of BeSe for UV optoelectronic applications