Memory effects in the frictional damping of diffusive and vibrational motion of adatoms

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Abstract
We investigate the memory effects in the frictional damping of the vibrational and diffusive motion of an adatom. Using the molecular-dynamics simulation method, we solve the equations of motion of an adatom in a periodic potential coupled to substrate phonons which are in turn coupled to a heat bath. The frustrated translational mode and the diffusion constant of the adatom is studied by calculating appropriate time-dependent correlation functions. We discuss our numerical results in the context of a generalized Langevin equation. The validity of analytic approximations to the memory function in the Langevin equation such as mode-mode coupling and initial value approximation are examined by comparing the analytic results with those obtained from the numerical simulations. © 1996 The American Physical Society.