Noncollinear Relativistic DFT+U Calculations of Actinide Dioxide Surfaces

A noncollinear relativistic PBEsol+U study of the low-index actinide dioxides (AnO₂, An = U, Np, Pu) surfaces has been conducted. The surface properties of the AnO₂ have been investigated and the importance of the reorientation of magnetic vectors relative to the plane of the surface is highlighted. In collinear nonrelativistic surface models, the orientation of the magnetic moments is often ignored; however, the use of noncollinear relativistic methods is key to the design of reliable computational models. The ionic relaxation of each surface is shown to be confined to the first three monolayers and we have explored the configurations of the terminal oxygen ions on the reconstructed (001) surface. The reconstructed (001) surfaces are ordered as (001)αβ < (001)α < (001)β in terms of energetics. Electrostatic potential isosurface and scanning tunneling microscopy images have also been calculated. By considering the energetics of the low-index AnO₂ surfaces, an octahedral Wulff crystal morphology has been calculated.