Generalized Langevin theory for gas/solid processes: Dynamical solid models

A new class of smooth and structured solid models is developed from the generalized Langevin theory of gas/solid processes S. A. Adelman and J. D. Doll, J. Chem. Phys. 64, 2375 (1976), and numerical results for scattering off the simplest of these model solids are presented. The models, which may be refined to arbitrary precision, allow one to treat the many-body or lattice effect in gas/solid dynamics in a qualitatively correct but computationally simple manner. Scattering calculations based on the models may be carried out using standard classical trajectory methodology; the many-body dynamics modifies the usual classical equations of motion through noise terms and auxiliary variables. Collisional studies based on the simplest of the new models reveal the importance of many-body dynamics on energy transfer and trapping thresholds. The percentage of energy transfer due to many-body effects is found to be a rapidly increasing function of solid Debye temperature ΘD; at ΘD≳225°K the many-body contribution to energy transfer often exceeds the uncoupled oscillator contribution. The threshold energy for trapping on the simplest model solid is often more than doubled due to many-body influence. Finally, helium scattering from silver is simulated and the results are compared with the measurements of Sau and Merrill.