Ab initio full-potential fully relativistic study of atomic carbon, nitrogen, and oxygen chemisorption on the (111) surface of δ-Pu

First-principles total-energy calculations within the framework of generalized gradient approximation to density-functional theory have been performed for atomic carbon, nitrogen, and oxygen chemisorption on the (111) surface of delta-Pu. The full-potential all-electron linearized augmented plane wave plus local orbitals method with the Perdew-Burke-Ernzerhof exchange-correlation functional has been employed. Chemisorption energies have been optimized with respect to the distance of the adatom from the Pu surface for four adsorption sites, namely, the top, bridge, hollow fcc, and hollow hcp sites, with the adlayer structure corresponding to a coverage of 0.50 of a monolayer in all cases. Computations were carried out at two theoretical levels, one without spin-orbit coupling (NSOC) and one with spin-orbit coupling (SOC). For NSOC calculations, the hollow fcc adsorption site was found to be the most stable site for C and N with chemisorption energies of 6.272 and 6.504 eV, respectively, while the hollow hcp adsorption site was found to be the most stable site for O with chemisorption energy of 8.025 eV. For SOC calculations, the hollow fcc adsorption site was found to be the most stable site in all cases with chemisorption energies for C, N, and O being 6.539, 6.714, and 8.2 eV, respectively. The respective distances of the C, N, and O adatoms from the surface were found to be 1.16, 1.08, and 1.25 angstrom. Our calculations indicate that SOC has negligible effect on the chemisorption geometries, but energies with SOC are more stable than the cases with NSOC within a range of 0.05-0.27 eV. The work function and net magnetic moments, respectively, increased and decreased in all cases upon chemisorption compared with the bare delta-Pu (111) surface. The partial charges inside the muffin tins, difference charge-density distributions, and the local density of states have been used to analyze the Pu-adatom bond interactions.