Hydrogen-mediated structural and electronic stabilization of cubic perovskite SrLiH₃ under extreme compression

This work presents a comprehensive first-principles investigation of the structural, mechanical, dynamical, vibrational, electronic, and bonding properties of SrLiH₃ under hydrostatic pressures up to 100 GPa. The relative stability of the cubic perovskite phase was evaluated against eight competing high-pressure candidate structures through enthalpy calculations. The results demonstrate that the cubic perovskite remains the thermodynamically favored phase throughout the investigated pressure range, with no pressure-induced structural transition. Mechanical stability is confirmed by the fulfillment of the generalized Born stability criteria, while phonon calculations reveal the absence of imaginary frequencies up to 100 GPa, establishing the dynamical stability of the structure. The pressure dependence of the infrared-active and silent phonon modes shows a systematic hardening of the high-frequency vibrations associated with the LiH₆ octahedra, indicating strengthened Li-H interactions under compression. Electronic structure calculations using the Heyd-Scuseria-Ernzerhof hybrid functional predict that SrLiH₃ remains an insulator, with the band gap increasing from 2.7 eV at ambient pressure to 3.3 eV at 100 GPa. Quantum theory-based analysis of the atomic basins reveals a pronounced contraction with increasing pressure, while the calculated atomic charges show only moderate changes and retain the clear charge separation between the cationic Sr and Li atoms and the anionic H atoms. Because the hydrogen sublattice occupies the largest fraction of the atomic volume, it makes the dominant contribution to the overall compressibility. These findings indicate that the predominantly ionic nature of cubic SrLiH₃ is preserved under compression, with the pressure response governed mainly by the collective contraction of the atomic basins rather than by significant pressure-induced charge redistribution. The combined thermodynamic, mechanical, vibrational, electronic, and topological analyses consistently indicate that cubic perovskite SrLiH₃ exhibits remarkable structural robustness and enhanced electronic stability under extreme compression, making it a promising model system for understanding the behavior of ionic complex hydrides at high pressure.