  Activated surface diffusion with interacting adsorbates is analyzed within
the Linear Response Theory framework. The so-called interacting single
adsorbate model is justified by means of a two-bath model, where one harmonic
bath takes into account the interaction with the surface phonons, while the
other one describes the surface coverage, this leading to defining a
collisional friction. Here, the corresponding theory is applied to simple
systems, such as diffusion on flat surfaces and the frustrated translational
motion in a harmonic potential. Classical and quantum closed formulas are
obtained. Furthermore, a more realistic problem, such as atomic Na diffusion on
the corrugated Cu(001) surface, is presented and discussed within the classical
context as well as within the framework of Kramer's theory. Quantum corrections
to the classical results are also analyzed and discussed.
