Electronic, optical, phonon properties, elastic, and the hydrogen storage density of CsXBr₃ (X: Be, Mg, Ca) perovskites: Ab-initio calculations and molecular dynamic (MD) simulation

Density functional theory (DFT) and molecular mechanics were employed to study the electronic structure, phonon density of state, dynamic stabilities, thermodynamics, desorption temperature and the hydrogen storage gravimetric density analysis of CsXBr₃ (X = Be, Mg, Ca) cubic perovskites. While the derived lattice constants were found to be in agreement with other experimental and theoretical works. The tolerance factor (T) and Molecular Dynamics (MD) simulation were analyzed in details to determine the halide perovskites structural and thermal stability respectively. Phonon density of state (Ph-DOS) and partial density of states (PDOS) showed the atomic orbital contributions and hybridization of some of the electronic states at the valence band minima (VBM) and conduction band maxima (CBM). Adopting the Quasi-Debye model, the thermodynamic properties were studied. The hydrogen storage potential of the studied perovskites was thoroughly investigated; the Bromine atoms of the studied perovskite were replaced with hydrogen atoms to form a new set of materials. The electronic properties showed direct band gap which is one of the criteria, indicating their suitability for hydrogen storage. The theoretically derived formation energy confirmed the perovskites high stability, portraying their suitability for hydrogen storage. The desorption temperature Tdes (°K) was obtained within an acceptable range of 329–381 K. Hence, it can be deduced that CsXH₃ is a better reversible hydrogen storage material.