The abnormal lattice contraction of plutonium hydrides studied by first-principles calculations

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 (PuH_x, 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 PuHx 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.