First-principles study of mechanical, electronic structure, optical, thermodynamic properties and hydrogen storage for new hydride perovskites XInH3 (X=Rb, Cs)*

The structure, mechanical, electronic, optical, thermodynamic properties and hydrogen storage capacities of XInH₃ (X = Rb, Cs) are simulated using the first-principles method. The calculated mechanical properties demonstrate that XInH₃ compounds own anisotropy, mechanical stability, and ductility. XInH₃'s interatomic bonds are ionic and bond stretching predominates in XInH₃ in accordance with Kleinman's parameter. The greater machinability index of RbInH₃ means that it is more suitable for machining. According to the electronic structures, XInH₃ are metallic. Analysis of their optical properties demonstrates that XInH₃ have good absorption properties in the UV range. Moreover, thermodynamic properties, including free energy, energy, entropy and heat capacity are also analyzed. Taking into account the formation energy, Born stability criterion and phonon dispersion curve, XInH₃ compounds show thermodynamic, mechanical, and dynamic stability. In addition, RbInH₃ and CsInH₃ have gravimetric hydrogen storage capacities with 1.466 and 1.191 wt%, respectively. These results are evidence that XInH₃ hydrides are potential candidate materials in the field of hydrogen storage. These investigations provide an important theoretical basis for further exploring the application of hydride materials in the field of hydrogen storage.