New Insights into the Crystal Structures of Plutonium Hydrides from First-Principles Calculations

One of the important research contents on hydrogen corrosion of plutonium is the determination of the complex crystal structures of plutonium hydrides and the bonding interactions between plutonium and hydrogen. However, it is very difficult to carry out the structural characterization of plutonium hydrides because of their high activity, high toxicity, and radioactivity. In this work, the crystal structures, lattice vibrations, and bonding properties of plutonium hydrides under ambient pressure are investigated by means of the density functional theory + <i>U</i> approach. Results show that PuH₃ exhibits many competition phase structures. After considering spin polarization, strong correlation (<i>U</i>), and spin–orbit coupling effects on the total energy and lattice dynamics stability, it is found that PuH₃ at ambient pressure is more likely to be hexagonal <i>P</i>6₃<i>cm</i> or trigonal <i>P</i>3<i>c</i>1 structure, instead of the usual supposed structures of hexagonal <i>P</i>6₃/<i>mmc</i> (LaF₃-type) and face-centered cubic (BiF₃-type). The calculated electronic structures clearly indicate that <i>P</i>6₃<i>cm</i> (<i>P</i>3<i>c</i>1) PuH₃ is a semiconductor with a small band gap about 0.87 eV (0.85 eV). The Pu–H bonds in Pu hydrides are dominated by the ionic interactions

Structural evolution and stability of plutonium oxide clusters

Plutonium oxide clusters have attracted great interest as potential complex for the separation or storage of radioactive plutonium elements. However, the structural stability, chemical bonding mechanism and maximum oxygen adsorption capacity for plutonium oxygen clusters are not well understood due to the difference between the radial distribution function and orbital energy of the plutonium atom. Here, we systematically study the structural evolution and electronic properties of plutonium oxygen clusters with cluster sizes n from 2 to 15 by using the CALYPSO cluster structural prediction method in combination with density functional theory (DFT) calculations. The low-lying isomers searched by the CALYPSO method are re-optimised at the theoretical level of B3LYP/ECP60MWB(Pu)/aug-cc-pVTZ(O). Relative stability results indicate that the PuO8 cluster with CS symmetry is the most stable cluster due to the large HOMO–LUMO gap (of 4.84 eV). The high stability of PuO8 cluster is predominantly attributed to the strong interactions between Pu-5f orbitals and O-2p orbitals. The Pu atom can chemically adsorb up to eight O atoms, and the corresponding adsorption energy is −3.84 eV. The present findings shed light on the complex chemical bonding and structural evolution mechanisms of plutonium oxide clusters, which may facilitate the rational design and the synthesis of other actinide-oxygen clusters. Plutonium chemically adsorbs eight oxygen atoms, and its high stability is attributed to the interactions between Pu-5f and O-2p orbitals.</p

Complex with Linear B–B–B Skeleton Trapped in Dinitrogen Matrix: Matrix Infrared Spectra and Quantum Chemical Calculations

The neutral (NN)–B–B–B–(N2) complex has been trapped in low-temperature dinitrogen matrix and identified by isotopic substitution and theoretical frequency calculations. The linear B–B–B skeleton is stabilized by two inequivalent N2, namely, one end-on and other side-on N2. The structure of linear B–B–B skeleton illustrates much difference from previously reported triangle configuration of B3 clusters. Frontier orbital analysis demonstrates that the σ orbital of end-on NN and the π-bonding orbital of side-on N2 acts as the donor orbital. π bonding character across B–B–B skeleton donates to the antibonding π* orbital of end-on NN and out of phase the B–B–B features π back-donation to antibonding π* orbital of side-on N2. The combination of strong σ-donating capacity coupled with a greater ability for accepting π-back-donation of the N2 ligand leads to the formation of (NN)–B–B–B–(N2) complex with linear B–B–B skeleton. In addition, complexes of (NN)B(NN), (NN)BB(NN), and (NN)B4(NN) have been identified in our experiments