DFT study of anti-perovskite hydrides X3NH3 (X=Mg, Sr) for hydrogen-storage applications

The structural, electronic, mechanical, optical, and thermodynamic properties of the anti-perovskite hydrides X 3 NH 3 (X = Mg and Sr) are systematically investigated using density functional theory (DFT) calculations within the CASTEP framework, with the aim of assessing their potential for hydrogen-storage and energy-related applications. The calculated negative formation energies, together with the absence of imaginary frequencies in the phonon spectra, confirm the thermodynamic and dynamical stability of both compounds, supporting their potential experimental realization. The predicted gravimetric hydrogen-storage capacities reach 4.40 wt% for Mg 3 NH 3 and 1.548 wt% for Sr 3 NH 3 , while the corresponding estimated hydrogen-desorption temperatures are 908 and 502 K, respectively. Both compounds exhibit semiconducting behavior and brittle mechanical characteristics, accompanied by pronounced elastic anisotropy. To improve the description of their electronic and optical properties, HSE06 hybrid-functional calculations were additionally performed. The HSE06 band-gap values are 3.245 eV for Mg 3 NH 3 and 0.195 eV for Sr 3 NH 3 , providing a more reliable assessment of their electronic structures. Moreover, the HSE06 optical response shows a behavior consistent with the PBE results, while providing an improved description of the electronic transitions and optical characteristics. In particular, both compounds exhibit significant optical absorption, dielectric response, reflectivity, and optical conductivity, highlighting their potential for optoelectronic and solar-energy applications. Finally, the thermodynamic analysis over the temperature range of 0–1000 K indicates favorable thermal behavior and provides further insight into their potential stability under practical operating conditions. Overall, the combined results suggest that Mg 3 NH 3 and Sr 3 NH 3 are promising multifunctional materials for hydrogen-storage and energy-related applications.