Computational exploration of hydrogen storage potential in Mg₂LiXH₆ (X = Ti, V) hydrides via DFT and AIMD simulations

Perovskite-based materials offer considerable potential for efficient, stable, and environmentally sustainable hydrogen storage technologies. In this study, an inclusive density functional theory (DFT) investigation was conducted to evaluate the structural, mechanical, electronic, optical, and thermodynamic features of Mg₂LiXH₆ (X = Ti, V) double perovskite hydrides. Both compounds adopt a stable cubic Fm-3m symmetry supported by favorable tolerance factors (0.87 for Ti and 0.92 for V) and negative formation energies (-1.15 and -1.27 eV per atom), confirming their thermodynamic stability. Both compounds exhibit thermal stability at 600 K without significant structural distortion, as confirmed by ab initio molecular dynamics (AIMD) simulations. Dynamic stability was evaluated using phonon dispersion calculations, which showed no imaginary frequencies, confirming that the system remains stable at 0 K. Mechanical analysis confirms elastic and Born stability, with Poisson's ratios of 0.31 (Mg₂LiTiH₆) and 0.24 (Mg₂LiVH₆) and B/G ratios of 2.35 and 1.61, indicating ductile behavior for Mg₂LiTiH₆ and a slightly brittle nature for Mg₂LiVH₆. Electronic structure calculations reveal metallic behavior while optical analyses indicate potential for optoelectronic applications. Both materials, Mg₂LiTiH₆ and Mg₂LiVH₆, exhibit promising hydrogen storage characteristics with gravimetric capacities of 5.28 and 5.14 wt% and estimated desorption temperatures of 425.55 and 467.23 K, respectively. These results showed that Mg₂LiXH₆ (X = Ti, V) are promising candidates for next-generation hydrogen storage and energy conversion systems.