  Diffusion studies of adsorbates moving on a surface are often analyzed using
2D Langevin simulations. These simulations are computationally cheap and offer
valuable insight into the dynamics, however, they simplify the complex
interactions between the substrate and adsorbate atoms, neglecting correlations
in the motion of the two species. The effect of this simplification on the
accuracy of observables extracted using Langevin simulations was previously
unquantified. Here we report a numerical study aimed at assessing the validity
of this approach. We compared experimentally accessible observables which were
calculated using a Langevin simulation with those obtained from explicit
molecular dynamics simulations. Our results show that within the range of
parameters we explored Langevin simulations provide a good alternative for
calculating the diffusion procress, i.e. the effect of correlations is too
small to be observed within the numerical accuracy of this study and most
likely would not have a significant effect on the interpretation of
experimental data. Our comparison of the two numerical approaches also
demonstrates the effect temperature dependent friction has on the calculated
observables, illustrating the importance of accounting for such a temperature
dependence when interpreting experimental data.
