First-principles investigation of XC- functionals and spin–orbit coupling in the LaPdBi Heusler alloy for energy harvesting applications

In this work, we present a comprehensive ab initio investigation of the half-Heusler alloy (h-HA) LaPdBi using density functional theory (DFT) with multiple exchange–correlation functionals, including PBE-GGA, LDA, TB-mBJ, HSE06, and spin–orbit coupling (SOC). Structural stability analysis confirms that the Y5 phase is the most stable configuration with a lattice constant of 6.9597 Å and negative formation energy, indicating thermodynamic stability. The calculated elastic constants satisfy the Born–Huang criteria, confirming mechanical stability and ductility. Electronic band structure results reveal a narrow direct band gap ranging from 0.15 eV (LDA) to 0.31 eV (HSE06), which reduces drastically to 0.06 eV under SOC. Effective mass calculations suggest higher electron mobility compared to holes, highlighting n-type doping as more favourable. Thermoelectric transport properties were analysed in the temperature range 100–1200 K. Both p-type and n-type LaPdBi exhibit promising Seebeck coefficients, with maximum ZT values approaching ∼1 at high temperatures. The results suggest that LaPdBi is a mechanically robust, thermally stable, and electronically tunable half-Heusler alloy with strong potential for mid-high temperature thermoelectric energy conversion. • LaPdBi stabilizes in Y5 phase with lattice constant 6.9597 Å. • Elastic constants confirm ductility and mechanical stability. • Narrow direct band gap (0.15–0.31 eV), reduced to 0.06 eV with SOC. • Effective masses favor n-type conduction for high mobility. • ZT reaches ∼1.0 for p-type at 800 K and ∼0.9 for n-type at 1200 K.