Structural, energetic and thermodynamic analyses of Ca(BH4)2·2NH3 from first principles calculations

Ca(BH4)2·2NH3 is a relatively new compound with potential application in hydrogen storage. Here the fundamental properties of the compound, such as electronic structure, energetic and thermodynamic properties, were comprehensively studied using first-principles calculations. Results from electronic density of states (DOS) and electron localization function (ELF) indicate the covalent bond nature of the N–H bond and the B–H bond. Charge density analyses show weak ionic interactions between the Ca atom and the NH3 complexes or the (BH4)− complexes. The calculated vibration frequencies of B–H and N–H are in good agreement with other theoretical and experimental results. Furthermore, we calculated the reaction enthalpy and reaction Gibbs free energy at a range of temperature 0–700 K. Our results are in good agreement with experimental results in literature. Possible reaction mechanism of the decomposition reaction is proposed.