Ab initio investigation of structural, electronic, mechanical, thermoelectric, and optical properties of laLiX (X = Si, ge) half-Heusler compounds

We present the first ab initio density functional theory study of 8-valence electron LaLiX (X = Si, Ge) half-Heusler compounds, investigating their structural, mechanical, electronic, phonon, thermoelectric, and optical properties. Formation energy calculations confirm thermodynamic stability, while Born–Huang criteria and ductility metrics (Pugh’s ratio, Cauchy pressure) reveal mechanical stability and deformability. Electronic structure calculations show indirect band gaps of 0.42 eV (LaLiSi) and 0.48 eV (LaLiGe), suggesting semiconductor behavior. Strong optical absorption in the visible region highlights optoelectronic potential. Boltzmann transport calculations predict promising thermoelectric performance, with near-unity figure of merit (ZT) at room temperature, indicating viability for energy conversion. These findings position LaLiSi and LaLiGe as novel multifunctional materials for optoelectronics and thermoelectric applications.