The diffusion pathways along the trough on the Si(001) surface are investig
ated by tight-binding molecular dynamics calculations using the environment
-dependent tight-binding silicon potential and by ab-initio calculations us
ing the Car-Parrinello method. A new diffusion pathway is discovered, consi
sting of rotation of the addimer. The energy barrier is calculated to be 1.
22 eV per dimer, which is in excellent agreement with the experiment. (C) 1
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