Investigating Stability, Thermomechanical, Optoelectronic, and Hydrogen Storage Potential of MgXH ₃ (X = Ga, Tl) Perovskites via DFT and AIMD Simulations

Hydride perovskites have attracted growing interest as solid-state hydrogen storage media due to their high density and safety. In this work, first-principles DFT and AIMD simulations are employed to investigate the structural, mechanical, electronic, optical, and thermodynamic properties of Mg-based hydrides MgXH 3 (X = Ga, Tl). Both compounds are confirmed to be stable, with AIMD results showing no structural deformation over 30 Ps at elevated temperatures. The hydrogen storage capacities are 3.12 wt % for MgGaH 3 and 1.30 wt % for MgTlH 3 . Mechanical analysis reveals ductile behavior with anisotropy, advantageous for accommodating volume changes during cycling. Electronic structure indicates metallic conductivity, where MgGaH 3, with stronger band dispersion, supports higher charge mobility and faster hydrogen kinetics, while MgTlH 3, with flatter bands, promotes controlled hydrogen release. Optical studies reveal high static dielectric response, strong absorption at low photon energies, and visible-range reflectivity exceeding reported thresholds for solar-heat reduction, highlighting potential in hydrogen storage, optoelectronic devices, and thermal-control coatings. Thermodynamic results suggest MgGaH 3 offers superior robustness for long-term storage, whereas MgTlH 3 facilitates easier release due to softer lattice dynamics. These findings underscore MgXH 3 (X = Ga, Tl) hydrides as promising multifunctional applications, combining solid-state hydrogen storage with optoelectronic and thermal-management applications, advancing pathways toward sustainable energy technologies.