  As a first step towards understanding the morphology of PdO crystals we
performed a systematic full-potential density-functional theory study of all
possible 1 x 1 terminations of the low-index surfaces of tetragonal PdO.
Applying the concept of first-principles atomistic thermodynamics we analyze
the composition, structure and stability of these PdO orientations in
equilibrium with an arbitrary oxygen environment. Within the studied subset of
1 x 1 geometries the polar PdO-terminated PdO(100) orientation turns out to be
surprisingly stable over the whole range of experimentally accessible gas phase
conditions. Setting up a constrained Wulff construction within the compiled
data set, this PdO(100)-PdO facet correspondingly dominates the obtained
polyhedron by far. The real PdO crystallite shape will however likely be
affected by surface reconstructions, which are not covered by the present
study.
