Diffusion of silicon addimer along the trough and from the trough to the to
p of dimer row on the Si(100) surface are investigated by tight-binding mol
ecular dynamics calculations using the environment-dependent tight-binding
silicon potential and by ab initio calculations using the Car-Parrinello me
thod. The studies discover new diffusion pathways consisting of rotation of
addimer. These new pathways have energy barriers in excellent agreement wi
th experiment data and are more energetically favorable than other diffusio
n pathways studied previously.