Ab initio molecular dynamics study of the interaction of plutonium with oxygen in the gas phase

Abstract

There are two kinds of plutonium surface corrosion, one of which is oxidation between plutonium and oxygen or oxygen compounds. To investigate the corrosion mechanism of plutonium with oxygen, density functional theory (DFT) calculations have been carried out in the present study to investigate the interaction of plutonium atoms with oxygen molecules. Considering all possible spin states, a comprehensive description of the reaction mechanism is presented. All minima and transition state structures along the reaction pathway are optimized and the interaction energies and equilibrium distances were evaluated. The nature of the Pu–O bonding mode evolution along the reaction pathways was further validated using electron localization function (ELF) calculations, which indicated that the interaction could be considered as an electrostatic interaction in the entrance channel and a strong covalent interaction in the exit channel. We analyzed the density of states (DOS) for the minima and transition states, for the sake of analyzing the contribution of 5f electrons/orbitals in the title reaction. The results indicate that the most of the contributions to the HOMO come from the 5f orbitals of the plutonium atoms. Furthermore, reaction rate constants computed between 298 and 1000 K using variational transition state theory (VTST) suggest that Wigner tunneling effects are generally large for the reactions considered. Additionally, product energy distributions for the title reaction were evaluated by carrying out direct classical trajectory calculations. The results demonstrate that most of the available energy appears as the vibration energy of the products. The outcomes of the current theoretical studies provide detailed insights for understanding the interaction of plutonium with oxygen molecules.