Computational Analysis of Tetragonal ThH₂ Hydride: Structural, Electronic, Mechanical, Thermodynamic, and Hydrogen Storage Capabilities for Future Energy Applications

Abstract

In this study, a comprehensive first-principles investigation has been carried out on ThH₂ to evaluate its structural, electronic, elastic, phonon, thermodynamic, and hydrogen storage properties. The calculations were performed using DFT within the framework of the GGA-PBE approximation, employing the CASTEP module. Structural optimization confirmed that ThH₂ crystallizes in a bct phase with space group I4/mmm, and the lattice parameters show good agreement with available experimental and computational data. Electronic band structure and DOS analyses reveal metallic behavior, with significant hybridization between Th-6d and H-1s orbitals. The elastic constants satisfy the mechanical stability criteria and indicate that ThH₂ is ductile and elastically anisotropic. Phonon dispersion confirms the dynamical stability of the compound, with no imaginary frequencies across the Brillouin zone. Temperature-dependent thermodynamic properties such as Debye temperature, Helmholtz free energy, entropy, enthalpy, and heat capacity were also evaluated using the quasi-harmonic approximation. The volumetric hydrogen storage capacity of ThH₂ (82.57 kg/m³) significantly exceeds the U.S. DOE’s 2025 target of 40 kg H₂/m³, demonstrating its strong potential to meet and surpass future storage requirements. The findings establish ThH₂ as a thermodynamically stable and mechanically robust material, making it a promising candidate for applications in advanced nuclear fuel systems and storage technologies.