Discrete-continuum hybrid model for dynamics with applications: Desorption of adsorbates and relaxation of lattice inclusions

The paper presents and extends an earlier model for the relaxation dynamics within solids and desorption of adsorbates on surfaces. The model retains the discrete nature of the adsorbates while adopting a continuum representation for the solid. Extensive one-dimensional model calculations are carried out along with sample calculations in the two-dimensional case. Specifically, in the one-dimensional case, the formulation is for a diatom with harmonic intramolecular bond and a Morse potential between the diatom and the remaining solid as well as an atomic inclusion in a two-dimensional bulk solid. The excitation mechanisms are initial disturbances that take the system away from its equilibrium configuration and acoustic pulses incident on the molecule. An extensive parametric study is carried out by varying the width, amplitude, and frequency content of the pulse along with the strength of the Morse bond. These calculations permit an understanding of the roles of the various parameters in determining the relaxation rate associated with energy transfer and desorption processes for the case of the diatom bound to the solid surface as well as an atom as a guest in the solid. The observed physical phenomena span the linear to the highly nonlinear regime.