HADBI MohammedDEMMOUCHE Kamel2026-01-192026-01-192026https://dspace.univ-temouchent.edu.dz/handle/123456789/6947This thesis investigates 18-electron half-Heusler compounds TiIrSb, ZrIrSb, TaIrGe, and TaIrSn in terms of their structural, electronic, optical, and thermoelectric properties using first-principles calculations. Particular emphasis is placed on the TiIrSb compound, where the effect of substituting titanium (Ti) atoms with zirconium (Zr) atoms in the 2 × 2 × 1 supercell on its physical properties, including dynamical stability, is examined, in addition to studying the influence of point defects of vacancy and antisite types on its structural, electronic, and optical stability. The VASP package, based on DFT, is employed with the PBE-GGA exchange– correlation functional, together with the Meta-GGA-SCAN functional to improve the accuracy of the predictions, while the calculations are performed within the supercell approach to assess the thermodynamic stability through formation energies and the dynamical stability through phonon calculations. Moreover, the hybrid functional HSE06 is used to investigate the electronic properties of the four compounds TiIrSb, ZrIrSb, TaIrGe, and TaIrSn, aiming at a more accurate description of the band gap and electronic structure.frHalf-Heuslerpoint defectsDFTVASP.Thesis