  Using a first-principles parameterized lattice-gas Hamiltonian we study the
adsorbate ordering behavior at atomic steps of a Pd(100) surface exposed to an
oxygen environment. We identify a wide range of gas-phase conditions comprising
near atmospheric pressures and elevated temperatures around 900 K, in which the
step is decorated by a characteristic O zigzag arrangement. For catalytic
processes like the high-temperature combustion of methane that operate under
these conditions our approach thus provides first insight into the structure
and composition at a prominent defect on the working surface.
