Van der Waals Interaction Really Matters: Energetics of Benzoic Acid on TiO2 Rutile Surfaces

Density functional theory (DFT) has been applied to elucidate the adsorption structures and energetics of benzoic acid on TiO2 (110), (100), and (011) rutile surfaces. We demonstrate that ab initio calculations of interacting carboxylic acids require an exchange-correlation functional with van der Waals (vdW) correction to yield reliable results, even for very small aliphatic species like acetic acid. On the (110) surface, benzoates dimerize due to intermolecular vdW interaction and form a 2 × 2 superstructure, which explains experimental findings already reported in the literature. The lateral vdW attraction between benzoates is even enhanced on (100) and (011) surfaces because of advantageous substrate periodicities, resulting essentially in only one geometrical adsorbate species.