Noncollinear Relativistic DFT + U Calculations of Actinide Dioxide Surfaces

A noncollinear relativistic PBEsol + U study of low-index actinide dioxides (AnO₂, An = U, Np, or Pu) surfaces has been conducted. The importance of magnetic vector reorientation relative to the plane of the surface is highlighted; this has often been ignored in collinear nonrelativistic models. 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.