First-principles calculations to investigate structural, electronic, mechanical, optical, vibrational, thermal properties, and hydrogen storage capabilities of Rb2SnH4 for hydrogen storage applications

Abstract

The structural, electronic, mechanical, optical, vibrational, and thermal properties of tetragonal Rb₂SnH₄ belonging to the space group P4₂/mnm as a hydrogen storage material, were meticulously examined using the ab initio method. The gravimetric hydrogen densities were determined as 2.77 wt%. The hydrogen desorption temperatures were measured at 29.05 K for Rb₂SnH₄. Electronic band structure computations yielded band gap values of 0.455 eV. The elevated band gap values indicate that Rb₂SnH₄ possesses semiconductor properties. The values of the second-order independent elastic constants, which indicate the hardness and mechanical stability of the materials, were computed. The values of the elastic constants indicated that Rb₂SnH₄ exhibits mechanical stability. Hardness characteristics, including bulk modulus, shear modulus, B/G ratio, Young's modulus, and Poisson's ratio, were computed utilizing the values of elastic constants. Based on the B/G ratio (1.764), Rb₂SnH₄ was identified as ductile material. Based on Poisson's ratio (0.262), the atoms in Rb₂SnH₄ compounds are interconnected by ionic bonds. Besides, the vibrational properties were also analyzed, and Rb₂SnH₄ is also dynamically stable as it has no negative branches. Furthermore, several optical parameters of Rb₂SnH₄, including dielectric function, conductivity, reflectivity, and absorption, were computed. Finally, the thermo-physical characteristics of this compound were computed.