Surface Diffusion and Chemical Reactions with KHIMERA
Quantitative information about surface diffusion of adsorbed particles and its chemical reactions is of crucial importance for kinetic modeling in heterogeneous catalysis, nanotechnology, and plasma chemistry.
Universal Set of Processes Accessible for Treating by KHIMERA
State of art models of surface processes incorporated into Khimera are based on qualitative physical ideas about the potential energy surfaces of the adsorbed particles and their dynamical interaction with phonons of the solid. Two approaches are used in the diffusion processes. One is based on the kinetic FokkerPlank equation and another is used the stochastic Langevin approach. Model of surface reaction in kinetic regime is based on wellapproved variant of statistical approach.
Example: surface diffusion Na/Cu(100)
The diffusion of sodium on copper is a practically important process in nanotechnology and has been studied in detail both experimentally and theoretically. The diffusion coefficient of this process was evaluated using the stochastic model of surface diffusion. This theory is applicable if the characteristic frequency of adatom vibration is lower than the Debye frequency.
The window of the Khimera module with the results of calculations of the diffusion coefficient using the Khimera module is presented in the figure along with the available experimental data.
Example: oxidization of CO on Pt
The reaction O+CO → CO2 on platinum is the limiting stage of heterogeneous oxidization of carbon monoxide. The rate constant of this reaction was evaluated using the transition state theory. In this case, the reaction activation energy should be lower than the diffusion activation energy.
The window of the Khimera module with the results of calculations of the rate constant using the Khimera module is presented in the figure along with the available experimental data. It is seen that the transition state theory with the parameters obtained from quantum chemical calculations provides a quantitative description of the direct bimolecular reaction.
Example: annealing of tungsten
The surface annealing is controlled by the trapping of diffusing adatoms by vacancies. The rate constant of this process for the tungsten surface was evaluated using the statistical model of surface diffusioncontrolled reactions. The results were obtained using the Khimera module and are presented in the figure along with the available experimental data. It is seen from the figure that the theory provides a quantitative description of the surface diffusioncontrolled reactions in a wide range of temperatures.
