Analysis of the origin of lateral interactions in the adsorption of small organic molecules on oxide surfaces

A decomposition scheme is proposed to analyze the physical contributions to the decrease in the binding energy of chemisorbed species with increasing coverage. This scheme is applied to the acetaldehyde–TiO

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(110) rutile system as a model for other small organic molecule—oxide surface systems. Different density functional theory (DFT) functionals have been employed at both low-medium and high coverages to understand how the different theoretical descriptions of the various terms influence the adsorbate–surface interaction. At low coverages, it is found that the localized adsorbate to surface electron donation is the fundamental physical process that influences the adsorbate–surface interaction. This results shows that while it is usually assumed that only pairwise adsorbate–adsorbate interactions influence the adsorption energy, the progressive modification of the surface properties (surface reduction in this case) may also play a significative role. The DFT+U functional results, in this case, in the best agreement with the experimental binding energy, and the inclusion of the dispersive forces results in largely overestimated adsorption energies. At higher coverages, the pure GGA and GGA+U functionals overestimate the repulsive terms and the computed binding energy is well below the experimental data. The inclusion of the dispersive forces is required to correctly reproduce the experimental results. The contributions of the different physical terms are also analyzed.