First-principles calculations on the crystal and electronic structures of LaNi 4.5Al 0.5H 6− xHe x ( [formula omitted], 0.5 and 1)

Abstract

The crystal structures and electronic properties of hydrides LaNi 4.5Al 0.5H 6− x He y ( 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 LaNi 4.5Al 0.5H 6 is the same as that of hydride LaNi 5H 6, 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 LaNi 4.5Al 0.5H 5.5He 0.5, 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 LaNi 4.5Al 0.5H 5He. 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.