Evaluating hydrogen storage potential of Cs2ABH6: DFT-based approach
Saadi Berri
Abstract
In the current investigation, we have implemented first-principles calculations to examine the structural, elastic, electrical and optical characteristics of Cs 2 AB H 6 (AB = AlGa, AlIn, AlTl, NaAl, NaGa, NaIn and TlIn). All of the calculations were performed out using first-principles density functional theory (DFT). The space group Fm -3 m (225) has been used. The computed values of lattice parameters are Cs 2 AlGaH 6 : 0.8739 nm, Cs 2 AlInH 6 : 0.8923 nm, Cs 2 AlTlH 6 : 0.8953 nm, Cs 2 NaAlH 6 : 0.8669 nm, Cs 2 NaGaH 6 : 0.8688 nm, Cs 2 NaInH 6 : 0.8960 nm, Cs 2 TlGaH 6 : 0.8938 nm and Cs 2 TlInH 6 : 0.9258 nm and also it is observed that the volume and density are inversely associated with each other. In addition, the computed band-gap values for Cs 2 AlInH 6 , Cs 2 AlTlH 6 , Cs 2 NaAlH 6 , Cs 2 NaGaH 6 , Cs 2 NaInH 6 , Cs 2 TlGaH 6 and Cs 2 TlInH 6 and Cs 2 YAuCl 6 are 1.21, 1.66, 2.58, 1.32, 1.42, 0.94 and 0.91 eV, respectively, which demonstrates the indirect semiconducting nature. Between 0 and 20 eV, optical spectra calculations are made, taking into account the real and imaginary parts of the dielectric function e(?), reflectivity R (?), index of refraction n (?), coefficients of extinction k (?) and absorption a(?). The dielectric function is wide close to the ultraviolet districts (3.10–4.13 eV). The extinction coefficient of the Cs 2 AB H 6 has the ability to worn for implements like Bragg’s reflectors, optical and optoelectronic equipments. The optical parameters of Cs 2 AB H 6 disclose that our working constructions have an elevated dielectric constant, with a greatest absorption in the visible range holding out over 2.45·10 5 cm -1 . All three compounds fulfil the Born stability condition. The gravimetric hydrogen storage capacities of Cs 2 AlInH 6 , Cs 2 AlTlH 6 , Cs 2 NaAlH 6 , Cs 2 NaGaH 6 , Cs 2 NaInH 6 , Cs 2 TlGaH 6 and Cs 2 TlInH 6 compounds are 1.64, 1.20, 1.88, 1.66, 1.48, 1.02, 1.11 and 1.20 wt.%, respectively. Cs 2 ABH 6 crystals are dynamically stable.