The alanates (complex aluminohydrides) have relatively high gravimetric hydrogen densities and are among the most promising solid-state hydrogen-storage materials.In this work,the electronic structures and the formation enthalpies of seven typical aluminum-based deuterides have been calculated by the plane-wave pseudopotential method,these being AlD 3,LiAlD 4,Li 3 AlD 6,BaAlD 5,Ba 2 AlD 7,LiMg(AlD 4) 3 and LiMgAlD 6.The results show that all these compounds are large band gap insulators at 0 K with estimated band gaps from 2.31 eV in AlD 3 to 4.96 eV in LiMg(AlD 4) 3.The band gaps are reduced when the coordination of Al varies from 4 to 6.Two peaks present in the valence bands are the common characteristics of aluminum-based deuterides containing AlD 4 subunits while three peaks are the common characteristics of those containing AlD 6 subunits.The electronic structures of these compounds are determined mainly by aluminum deuteride complexes (AlD 4 or AlD 6) and their mutual interactions.The predicted formation enthalpies are presented for the studied aluminum-based deuterides.
Pu can be loaded with H forming complicated continuous solid solutions and compounds,and causing remarkable electronic and structural changes.Full potential linearized augmented plane wave methods combined with Hubbard parameter U and the spin-orbit effects are employed to investigate the electronic and structural properties of stoichiometric and non-stoichiometric face-centered cubic Pu hydrides(PuHx,x=2,2.25,2.5,2.75,3).The decreasing trend with increasing x of the calculated lattice parameters is in reasonable agreement with the experimental findings.A comparative analysis of the electronic-structure results for a series of PuH x compositions reveals that the lattice contraction results from the associated effects of the enhanced chemical bonding and the size effects involving the interstitial atoms.We find that the size effects are the driving force for the abnormal lattice contraction.
We perform first-principles calculations to investigate the structural, magnetic, electronic, and mechanical properties of face-centered cubic (fcc) PuH 2 and fcc PuH 3 using the full potential linearized augmented plane wave method (FP-LAPW) with the generalized gradient approximation (GGA) and the local spin density approximation (LSDA) taking account of both relativistic and strong correlation effects. The optimized lattice constant a0 = 5.371 for fcc PuH2 and a0 = 5.343 for fcc PuH3 calculated in the GGA + sp (spin polarization) + U (Hubbard parameter) + SO (spin-orbit coupling) scheme are in good agreement with the experimental data. The ground state of fcc PuH3 is found to be slightly ferromagnetic. Our results indicate that fcc PuH2 is a metal while fcc PuH3 is a semiconductor with a band gap about 0.35 eV. We note that the SO and the strong correlation between localized Pu 5f electrons are responsible for the band gap of fcc PuH3 . The bonds for PuH2 have mainly covalent character while there are covalent bonds in addition to apparent ionicity bonds for PuH3 . We also predict the elastic constants of fcc PuH2 and fcc PuH3 , which were not observed in the previous experiments.
