Figure 2: (a) A schematic drawing of Pt(997) around the step and its PES with ES barrier . Sites 1, 2, and 3 are the HS site, HT site next to the BS site, and BS site, respectively. is the NO does not adsorb, is the hcp-hollow site next to the HS site. is the rate constant to migrate from a hollow site to a neighboring hollow site on the terrace. (b), (c) Models of PES in the KMC simulation. In model A, the rate constant from site 1 to site 3 is assumed to be the same as that from site 2 to site 3. In model B, the rate constant from site 1 to site 3 is assumed to be zero (infinite barrier).