Determination of coverage-dependent surface reaction rates using λ-dynamics: Application to molecular desorption

In this work, we extend the λ-dynamics method to surface processes. In particular, we introduce a way to calculate free-energy change for a surface process and the potential of mean force if needed. The method is demonstrated for NO desorption from a Pd(111) surface. It is further applied to CO desorption from Rh(111) at several coverages, using an accurate machine learned potential energy surface. Comparison with experimental results indicates that the coverage dependence of the desorption rate is well reproduced, but the absolute desorption energy still contains significant uncertainties. The larger desorption rate coefficient at higher coverages is attributed largely to repulsive interaction between CO adsorbates on the surface.