  We present the results of a density functional theory (DFT) investigation of
the surfaces of rutile-like vanadium dioxide, VO2(R). We calculate the surface
energies of low Miller index planes, and find that the most stable surface
orientation is the (110). The equilibrium morphology of a VO2(R) particle has
an acicular shape, laterally confined by (110) planes and topped by (011)
planes. The redox properties of the (110) surface are investigated by
calculating the relative surface free energies of the non-stoichiometric
compositions as a function of oxygen chemical potential. It is found that the
VO2(110) surface is oxidized with respect to the stoichiometric composition,
not only at ambient conditions but also at the more reducing conditions under
which bulk VO2 is stable in comparison with bulk V2O5. The adsorbed oxygen
forms surface vanadyl species much more favorably than surface peroxo species.
