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 using the environment-dependent tight-binding silicon potential and by ab initio calculations using the Car-Parrinello method. The studies discover a new diffusion pathway consisting of the rotation of the ad-dimer. The calculated energy barrier is in excellent agreement with experiment and is much more energetically favorable than other diffusion pathways by parallel and perpendicular ad-dimers.