High-temperature tight-binding molecular dynamics simulations were performed, as well as 0K calculations, in order to study the motion of the surface dimers near to various types of step. These results were compared with the corresponding results for dimers in a clean terrace, far from any defect. It was found that the dimers in step A edge flip slower than those in a clean surface, in agreement with scanning tunnelling microscopic observations, while those in rebounded step B edge flip faster. These differences in the energy barriers were reflected in the electronic structures, in particular in the local density of states near to the energy gap. Finite temperature and 0K calculations predicted the same relevant flipping barriers for dimers near step A edge, but the agreement was not as good for dimers close to rebounded step B edge, where correlated flipping events were important. In this case, finite temperature molecular dynamics simulations were more efficient in estimating the effective barrier. Some similarities in the dynamics were found between dimers close to single-dimer vacancies, steps and steps with kinks. First neighbours of an single-dimer vacancies, upper step B edge dimers, and dimers close to kinks in step A had similar local environments. Therefore all tended to flip faster, and spent most of the time in a symmetrical state. On the other hand, second-nearest neighbours of a single-dimer vacancies, upper step A edge dimers, and dimers close to kinks in step B tended to flip slower.

Theoretical Study of the Role of Surface Defects on the Dimer Dynamics on Si(001). C.C.Fu, A.Saúl: Surface Science, 2003, 527[1-3], 113-23