Diffusion and vibration of adatoms on a solid surface

A microscopic theory for the diffusive and vibrational motion of absorbed atoms on a solid surface is presented. We evaluate and analyze the dynamical structure factor. The quasielastic scattering peak is found to consist of mixed contributions from both diffusion and vibration. The vibrational peak in the dynamic structure factor indicates both a shift and broadening from anharmonic effects and frictional damping. Applied to Na on Cu(001) surface, the theory agrees quantitatively with recent experimental measurements.