Single Particle Trajectory Analysis for the Evaluation of Surface Accommodation Coefficients

The direct simulation Monte-Carlo method utilizes gas-surface interaction models (GSI) like the Maxwell model and the Cercignani-Lampis-Lord model (CLL) to perform gas-surface interactions. Accommodation coefficients (ACs), which quantify the efficiency of momentum and energy transfer at the surface are the input parameters for such GSI models. This work utilizes the molecular dynamics (MD) method to study the interactions between gas and surface to obtain surface ACs. A simulation strategy that mimics a scattering experiment is developed to obtain these ACs. A large number of gas molecules are made to collide (one at a time) with the surface, and the resulting distributions of the scattered molecules are statistically averaged to calculate ACs. Comments are made regarding the applicability of this method by comparing the velocity and directional distributions of the scattered molecules with that of the CLL model. The simulations are performed by considering noble gases in combination with graphite and platinum surfaces. The effect of parameters like the chemical species of gas, and the bulk velocity of gas molecules on the ACs are also investigated in detail.