First principles study of influence of exchange-correlation functionals on the electronic, optical and thermoelectric transport properties of XCoGe (X = V, Nb, Ta) half-Heusler alloys

Half-Heusler alloys have attracted considerable interest for high-temperature thermoelectric waste recovery and optoelectronic applications due to their tunable electronic structures, mechanical stability and favorable transport behavior. In this work, we investigated how the choice of exchange correlation functionals influences the electronic, optical and thermoelectric transport properties of XCoGe (X = V, Nb, Ta) using first-principles calculations within the PBE-GGA, GGA + U and TB-mBJ frameworks. All compounds are confirmed to be mechanically stable, non-magnetic indirect semiconductors crystallizing in the cubic F-43m phase. Optical analysis revealed prominent absorption extending from the visible to ultra-violet spectra, accompanied by moderately high dielectric constants, reflectivity and refractive indices. The thermoelectric transport response exhibited strong dependence on the exchange-correlation treatment and carrier concentration optimization. Among the investigated compounds, TaCoGe displayed the highest thermoelectric performance with peak ZT of 0.93 at 1500 K, while VCoGe and NbCoGe efficiencies were limited by bipolar conduction at higher temperatures.