First-principles LDA + U calculations investigating the lattice contraction of face-centered cubic Pu hydrides

Plutonium metal can be loaded with hydrogen, which forms complicated solid solutions and compounds, and leads to significant changes in electronic structure. A first-principles pseudopotential plane wave method with added Hubbard parameter U was employed to investigate the electronic and structural properties of face-centered cubic Pu hydrides (PuHx, x = 2, 2.25, and 3). The decrease in calculated lattice parameters with increasing x is in reasonable agreement with experimental findings. Comparative analysis of the electronic-structure results for a series of PuHx compositions reveals that lattice contraction occurs due to enhanced chemical bonding and the size effects involving interstitial atoms. We find that the size effects are the driving force for the abnormal lattice contraction.