Title of article :
Adsorption and diffusion of oxygen atom on UN2(100) surface and subsurface: a density functional theory study (DFT and DFT + U)
Author/Authors :
Zergoug, T Nuclear Research Center at Draria (CRND) - Algiers, Algeria , Abaidia, S. E. H M’Hamed Bouguerra University - Boumerdes, Algeria , Nedjar, A Nuclear Research Center at Draria (CRND) - Algiers, Algeria , Mokeddem, M. Y M’Hamed Bouguerra University - Boumerdes, Algeria
Abstract :
In the present work, adsorption and diffusion of
oxygen (O) atom on uranium dinitride (UN2) is studied to
map out the preferential UN2(100) surface site. The first
principle method based on density functional theory (DFT)
within the generalized gradient approximation PBE and the
covariant version energy functional PBE ? U correction
were used. The supercell approach and a coverage dependence
of the adsorption structures and energetic were
studied in detail for several monolayers’ (ML) range.
Potential energy surfaces (PES) corresponding to the
interaction between O atom and UN2(100) on surface and
subsurface for several sites and layers (Top U and Top N
slabs) were calculated and favorable sites were identified
with their maxima energy stable positions, which were then
analyzed. For all positions, the PES show the same system
behavior, when the O atom is sufficiently far from the UN2
surface, and the energy of the system tends to the sum of
free UN2 slab and free oxygen atom energies. In return,
when the distances decrease, strong interactions appear
with presence of important potential wells. Calculation
results showed that favored on-surface site for O atom
adsorption were found to be near the bridge one for the UN
(Top U slab) corresponding to five layers, uranium terminated
and top one for (Top N slab) corresponding to six
layers nitrogen terminated, the maximum system energy is
situated at a position of about 1.2 and 1.5 A ° from the
surface for the two layers types calculations respectively.
For subsurface results, only Top N presents a favorable
incorporation site at the hollow position and the penetration
of O atom is about -0.5 A ° from the surface. DFT ? U
study confirms all the results obtained by DFT calculations;
that is, the maxima site positions for oxygen atom and the
adhesion energy values per atom are of the same order of
magnitudes. The adsorption energy per oxygen atom and
the mean distance from the top surface gradually decrease
with the coverage of O atoms for both on-surface cases, Top
U and Top N slabs, with oxygen occupying the favorable
site. For the Top N slab hollow site, the incorporation of
oxygen through the surface becomes effective from a coverage
of 3/8 ML with an encrustation of about -0.3 A ° .
Keywords :
Uranium dinitride (UN2) , DFT , DFT + U , Adsorption , Coverage
Journal title :
Astroparticle Physics
