Compressive Strain Unlocks Rapid Hydrogen Desorption in XH ₂ With X = Mg, Nb, and V via Interstitial Pauli Repulsion

Rutile MgH ₂ and fluorite VH ₂ and NbH ₂ are studied by GPAW/PBE density functional theory calculations under isotropic strain ε . By applying Birch–Murnaghan–van’t Hoff fitting procedures and the van’t Hoff screening method, we obtain a MgH ₂ desorption temperature of 412 K and corresponding VH ₂ and NbH ₂ values of 453 and 576.5 K. Under compressive strain, these temperatures are reduced by up to 93 K, 200 K, and 259 K, respectively. Finite‐difference phonon calculations show that VH ₂ is dynamically stable for the entire range of ε , while MgH ₂ and NbH ₂ become dynamically unstable on the H sublattice when compressed to −5%. We conclude that the destabilization is mainly due to the interaction of hydrogen with the metal d ‐orbitals. Langevin dynamics calculations at a temperature of 1300 K confirm the kinetic importance of strain: the mean compression‐to‐tension onset time ratio ( n  = 3 independent trajectories per strain state) is 3.39 for VH ₂ , 4.93 for NbH ₂ , and 3.04 for MgH ₂ . MgH ₂ is an ionic reference that uniquely establishes the structural threshold for the onset of interstitial Pauli repulsion in open fluorite lattices.