Theoretical investigation of oxygen adsorption on Pu-Ga alloy (111) surface

All electron density functional theory was implemented to study the adsorption of atomic oxygen on a 3.125 at. {\%} Ga stabilized $\delta $-Pu (111) surface. A 4-layer periodic slab, with 8 atoms per layer, was used to model the surface, and the location of the Ga within the surface was considered. High symmetry on-surface and interstitials adsorption sites were explored, which also included the adatom placed in different local environments (i.e. oxygen coordinated with/without a Ga atom). Full relaxation of the atomic positions of the Pu-Ga slab and O atom were employed. The inclusion of spin-orbit-coupling was preformed for the lowest energetic structure. The goal of these calculations was to the probe the effects that Ga may have within the surface when O is adsorb. We found that oxygen binds strongly at an on-surface site with chemisorption energy of -5.06 eV and prefers to be three-fold coordinated in a Pu-rich environment. However, when Ga is participating in chemical bonding with the O adatom chemisorptions energies were unfavorable. Interstitials sites were also unfavorable, which implies that diffusion of O into the subsurface is an activated process. Furthermore, a geometric analysis of the slab after O adsorption showed local oxygen-induced distortions, which will be discussed in detail.