Ad-dimer diffusion between trough and dimer row on Si(100)

The diffusion pathways between the trough and the dimer row on the Si(100) surface are investigated by tight-binding molecular dynamics calculations u sing the environment-dependent tight-binding silicon potential and by ab in itio calculations using the Car-Parrinello method. The studies discover a n ew diffusion pathway consisting of the rotation of the ad-dimer. The calcul ated energy barrier is in excellent agreement with experiment and is much m ore energetically favorable than other diffusion pathways by parallel and p erpendicular ad-dimers.