Ab initio investigation of the structural, mechanical, electronic, thermodynamic, and optical properties of V₂FeNiGe₂ and Hf₂FeNiSb₂ double half-Heusler compounds

In the present work, using ab initio density-functional theory methods based on the Quantum ESPRESSO package, we have investigated the structural, elastic, electronic, and optical properties of 18-electron V 2 FeNiGe 2 and Hf 2 FeNiSb 2 double half-Heusler alloys. The calculated elastic properties suggest a ductile behavior with metallic bonding for V 2 FeNiGe 2 and a brittle behavior with covalent bonding for Hf 2 FeNiSb 2 . The thermodynamic properties (Debye temperature, melting temperature) are also predicted and discussed for the studied alloys. The alloys are found to be semiconducting with indirect band gaps of 0.53 eV for V 2 FeNiGe 2 and 0.47 eV for Hf 2 FeNiSb 2 . We also computed and analyzed their optical properties (dielectric function, optical conductivity, refractive index, absorption index, and reflectance) and our calculations suggest that both materials have high absorption coefficient and optical conductivity in the UV as well as visible region. The results make them potential candidates for the manufacture of opto-electronic devices.