Theoretical investigation on the H sublattice in CaH₆ and energetic performance

Metal superhydride compounds (MSHCs) have attracted much attention in the fields of high-pressure physics due to the superconductivity properties deriving from the metallic-hydrogen-like characteristics and relatively mild synthesis conditions. However, their energetic performance and related potential applications are still open issues till now. In this study, CaH₆ and NbH₃, which exhibit evidently differences in their geometric and electronic structures, were chosen as examples of MSHCs to investigate their energetic performance. The structure, bonding features and energetic performance of CaH₆ and NbH₃ were predicted based on first-principles calculations. Our results reveal that high-pressure MSHCs always exhibit high energy densities. The range of theoretical energy density of CaH₆ was predicted as 2.3-5.3 times of TNT, while the value for NbH₃ was predicted as 1.2 times of TNT. Our study further uncover that CaH₆ has outstanding energetic properties, which are ascribed to the three-dimensional (3D) aromatic H sublattice and the strong covalent bonding between the H atoms. Moreover, the detonation process and products of rapid energy-release stage of CaH₆ were simulated via AIMD method, based on which its superior combustion performance was predicted and its specific impulse was calculated as 490.66 s. This study not only enhances the chemical understanding of MSHCs, but also extends the paradigm of traditional energetic materials and provides a new route to design novel high energy density materials.