Ab initio studies of A2PtH6 (A = K,Rb) materials for hydrogen storage purposes and optoelectronic applications

•Rb2PtH6 and K2PtH6 are X-X direct gap semiconductors.•The band-gap energies for Rb2PtH6 and K2PtH6 are found to be 7.053 and 5.608 eV, respectively.•Rb2PtH6 and K2PtH6 materials show a high optical absorption coefficient over a wide absorption band.•A comparison between the electronic properties and optical spectra of Rb2PtH6 and K2PtH6 materials has been made. A2PtH6 (A = K,Rb) are reported to be promising materials for hydrogen storage and optoelectronics. This contribution deals with band structure, structural and elastic properties, phonon spectra, mechanical and dynamical stabilities, hydrogen storage properties, and optical responses of Rb2PtH6 and K2PtH6 compounds. The computations are carried out using first-principles all electrons density-functional calculations. The authors results regarding the recorded bulk modulus of the materials under focus indicate that Rb2PtH6 has higher resistivity against volume change than K2PtH6. Both materials under focus are found to be stable mechanically and dynamically and ductile in nature. The present band structure calculations showed that Rb2PtH6 and K2PtH6 are X-X wide direct gap semiconductors with band-gap energies of 7.053 and 5.608 eV, respectively. The gravimetric hydrogen density and the hydrogen desorption temperature are recorded as 1.62 wt% and 803.44 K, respectively for Rb2PtH6 and 2.16 wt% and 799.38 K, respectively for K2PtH6. The material Rb2PtH6 has been found to have a static refractive index n(0) of 1.17 and a static dielectric constant ε(0) of 1.38, while K2PtH6 has values of n(0) = 1.50 and ε(0) = 2.25. Both compound materials of interest show a high optical absorption coefficient with a wide absorption band.