For the cluster models, the adsorption energies and the resulting slopes in Figure show some deviation from the values for the periodic systems. This is expected partly because of the different basis functions in use (plane wave vs atom-centered Gaussian functions) and partly because of the truncated sizes for the clusters. After all, the adsorption energies of adsorbates on transition metal clusters can exhibit some oscillation as the size of the cluster grows towards a full, infinite surface. Despite the differences, the general trends of the scaling relations for the periodic systems are reproduced well by the cluster model resulting in Figure , with the fitted slopes of 0.68, 0.53, 0.46, and 0.01, respectively, for the CH x adsorbates, an MAE up to 0.22 eV from the linear fitting values, and an R 2 value of 0.96 or higher for CH x (x = 1, 2, 3). This establishes the validity of using the truncatedmetal clusters as surrogate models for the periodic surfaces for carrying out further energy decomposition analysis.