First-principles calculations on the crystal and electronic structures of LaNi4.5Al0.5H6−xHex (, 0.5 and 1)

The crystal structures and electronic properties of hydrides LaNi4.5Al0.5H6−xHey ( x = 0 , 0.5 , 1.0 ) have been investigated by means of the density functional theory using the full-potential linearized augmented plane wave (FLAPW) method with the generalized gradient approximation (GGA). The calculated data indicate that the micro-arrangement of hydrogen atoms in LaNi4.5Al0.5H6 is the same as that of hydride LaNi5H6, which is consistent with the experimental results in terms of the equilibrium desorption isotherms. And we found that once the first He atom locates in the tetrahedral interstitial sites (6m site) near Al atom for LaNi4.5Al0.5H5.5He0.5, then it is difficult for the second He atom to locate in the 6m site again. Therefore, the second He atom would prefer to occupy the middle plane site (6m\ast site) apart from Al atom for LaNi4.5Al0.5H5He. To study the interaction among La, Ni, Al, H and He atoms, the figures referring to the densities of states and contour maps of the electron densities on two different planes are analysed.