Adsorption and dissociation of molecular oxygen on α-Pu (0 2 0) surface: A density functional study

Molecular and dissociative oxygen adsorptions on the α-Pu (0 2 0) surface have been systematically studied using the full-potential linearized augmented-plane-wave plus local orbitals (FP-LAPWlo) basis method and the PerdewBurkeErnzerhof (PBE) exchange-correlation functional. Chemisorption energies have been optimized for the distance of the admolecule from the Pu surface and the bond length of OO atoms for four adsorption sites and three approaches of O₂ admolecule to the (0 2 0) surface. Chemisorption energies have been calculated at the scalar relativistic level with no spinorbit coupling (NSOC) and at the fully relativistic level with spinorbit coupling (SOC). Dissociative adsorptions are found at the two horizontal approaches (O₂ is parallel to the surface and perpendicular/parallel to a lattice vector). Hor2 (O₂ is parallel to the surface and perpendicular to a lattice vector) approach at the one-fold top site is the most stable adsorption site, with chemisorption energies of 8.048 and 8.415 eV for the NSOC and SOC cases, respectively, and an OO separation of 3.70 Å. Molecular adsorption occurs at the Vert (O₂ is vertical to the surface) approach of each adsorption site. The calculated work functions and net spin magnetic moments, respectively, increase and decrease in all cases upon chemisorption compared to the clean surface. The partial charges inside the muffin-tins, the difference charge density distributions, and the local density of states have been used to investigate the Pu-admolecule electronic structures and bonding mechanisms.