  We present a density-functional theory based Wulff construction of the
equilibrium shape of RuO2 particles in an oxygen environment. The obtained
intricate variations of the crystal habit with the oxygen chemical potential
allow for a detailed discussion of the dependence on the oxidizing pretreatment
observed in recent powder catalyst studies. The analysis specifically indicates
an incomplete particle shape equilibration in previously employed low
temperature calcination. Equilibrated particles could be active CO oxidation
catalysts with long-term stability in oxidizing feed and then represent an
interesting alternative to the previously suggested core-shell concept.
