First‐Principles Investigation of Stable Rare‐Earth Perovskite TmLiH3 and YbLiH3 Hydrides for Solid‐State Hydrogen Storage
First‐principles density functional theory (DFT) computations were conducted to examine the structural, electrical, optical, mechanical, and hydrogen storage properties of the rare‐earth‐based perovskite hydrides XLiH3 (X = Tm, Yb). The cubic structures were optimized in space group Pm3¯m$Pm\bar{3}m$ with approximately equal lattice parameters (∼3.61 Å; ∼47 Å3). The stability of the cubic framework aligns with tolerance and octahedral factor criteria. Thermodynamic stability is evidenced by the negative formation energies of −0.489 and −0.456 eV/atom for TmLiH3 and YbLiH3, respectively. The electronic structure analysis demonstrates metallic characteristics, indicating improved electrical conductivity and efficient charge transfer. The compounds demonstrate strong mechanical, dynamic, and thermal stability, confirmed by standard elastic‐stability assessments, phonon analyses, and ab initio molecular dynamics stability at around 300 K. The evaluation of hydrogen storage reveals gravimetric capacities of 1.69 wt.% for TmLiH3 and 1.65 wt.% for YbLiH3, with substantial volumetric capacities of 107 and 107.1 g H2/L, respectively, and suitable desorption temperatures of 381.36 and 336.69 K.