Electronic Structures and Bonding of Oxygen on Plutonium Layers

Oxygen adsorption on delta-Pu (100) and (111) surfaces have been studied at both non-spin-polarized and spin-polarized levels using the generalized gradient approximation of density functional theory (GGA-DFT)with Perdew and Wang functionals. The center position of the (100) surface is found to be the most favorable site with chemisorption energies of 7.386 eV and 7.080 eV at the two levels of theory. The distances of the oxygen adatom from the Pu surface are found to be 0.92A and 1.02A, respectively. For the (111) surface non-spin-polarized calculations, the center position is also the preferred site with a chemisorption energy of 7.070 eV and the distance of the adatom being 1.31A, but for spin-polarized calculations the bridge and the center sites are found to be basically degenerate, the difference in chemisorption energies being only 0.021 eV. In general, due to the adsorption of oxygen, plutonium 5f orbitals are pushed further below the Fermi energy, compared to the bare plutonium layers. The work function, in general, increases due to oxygen adsorption on plutonium surfaces.Comment: Spin-polarization is considered, and the paper is revised accordingl

A density functional study of molecular oxygen adsorption and reaction barrier on Pu (100) surface

Oxygen molecule adsorptions on a Pu (100) surface have been studied in detail, using the generalized gradient approximation to density functional theory. Dissociative adsorption with a layer by layer alternate spin arrangement of the plutonium layer is found to be energetically more favorable compared to molecular adsorption. Hor2 approach on a bridge site without spin polarization was found to the highest chemisorbed site with energy of 8.787 eV among all the cases studied. The second highest chemisorption energy of 8.236 eV, is the spin-polarized Hor2 or Ver approach at center site. Inclusion of spin polarization affects the chemisorption processes significantly, non-spin-polarized chemisorption energies being typically higher than the spin-polarized energies. We also find that the 5f electrons to be more localized in spin-polarized cases compared to the non-spin-polarized counterparts. The ionic part of O-Pu bonding plays a significant role, while the Pu 5f-O 2p hybridization was found to be rather week. Also, adsorptions of oxygen push the top of 5f band deeper away from the Fermi level, indicating further bonding by the 5f orbitals might be less probable. Except for the interstitial sites, the work functions increase due to adsorptions of oxygen

Modeling the actinides with disordered local moments

A first-principles disordered local moment (DLM) picture within the local-spin-density and coherent potential approximations (LSDA+CPA) of the actinides is presented. The parameter free theory gives an accurate description of bond lengths and bulk modulus. The case of $\delta$-Pu is studied in particular and the calculated density of states is compared to data from photo-electron spectroscopy. The relation between the DLM description, the dynamical mean field approach and spin-polarized magnetically ordered modeling is discussed.Comment: 6 pages, 4 figure

A Density Functional Study of Atomic Hydrogen Adsorption on Plutonium Layers

Hydrogen adsorption on delta-Pu (100) and (111) surfaces using the generalized gradient approximation of the density functional theory with Perdew and Wang functionals have been studied at both the spin-polarized level and the non-spin-polarized level. For the (100) surface at the non-spin-polarized level, we find that the center position of the (100) surface is the most favorable site with a chemisorption energy of 2.762 eV and an optimum distance of the hydrogen adatom to the Pu surface of 1.07 A. For the spin-polarized (100) surface, the center site is again the preferred site with a chemisorption energy of 3.467 eV and an optimum hydrogen distance of 1.13 A. For the non-spin-polarized (111) surface, the center position is also the preferred site, but with slightly lower chemisorption energy, namely 2.756 eV and a higher hydrogen distance, 1.40 A, compared to the (100) center site. The center site is also the preferred site for the spin-polarized (111) surface, with a chemisorption energy of 3.450 eV and a hydrogen distance of 1.42 A. Also, for the spin-polarized calculations, the over all net magnetic moments of the (111) surface changed significantly due to the hydrogen adsorption. The 5f orbitals are delocalized, especially as one approaches the Fermi level. However, the degree of localization decreases for spin-polarized calculations. The coordination numbers have a significant role in the chemical bonding process. Mulliken charge distribution analysis indicates that the interaction of Pu with H mainly takes place in the first layer and that the other two layers are only slightly affected. Work functions, in general, tend to increase due to the presence of a hydrogen adatom.Comment: The introduction is extended to include a short review of delta-P