(683d) Cluster-Expansion-Based Modeling of the Coverage Dependence of Adsorbate Binding at a Metal Surface

The binding of adsorbates to surfaces is often characterized using mean field models. This approach treats adsorbate binding energies as constant independent of coverage and neglects and correlations between the locations of adsorbates. In this work, we use lattice-based cluster expansions to model the configuration-dependent energetics of oxygen adsorption on the Pt(111) surface. The cluster expansions were parameterized using DFT calculations of 49 distinct configurations, the convergence of the expansion with cluster and configuration size evaluated, and the relative contributions of electronic and relaxation effects to adsorbate interactions evaluated. The cluster expansion was used in concert with Monte Carlo simulations to model adsorbate chemical potential as a function of surface coverage and temperature. The binding energy was found to be roughly linear with respect to the surface coverage, consistent with earlier studies. Ordered states were found at ¼, ½, and 2/3 ML coverage. Binding energy distributions were calculated using the cluster expansion and snapshots from the Monte Carlo simulations. Binding energy distributions of ordered structures can be identified by the presence of large spikes at specific binding energies, while disordered structures were identified by their low and broad distributions.