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DFT Studies of Adsorption of Benzoic Acid on the Rutile (110) Surface: Modes and Patterns

Adsorption of benzoic acid on the (110) surface of rutile, both unreconstructed and (1x2)- reconstructed ones, at saturation coverage of one benzoate per two adjacent five-coordinated Ti5c sites has been studied using DFT simulations, as implemented through the Vienna Ab initio Simulations Package (VASP). In order to study the effects of hydrogen bonding and Van der Waals forces in influencing the relative stabilities of different adsorbate overlayer superstructures, these studies were performed through Local Density Approximation (LDA), Generalized Gradient Approximation(GGA) and DFT-D2. Through the calculations, it was found out that although the optimized structures corresponded with the proposed models for the experimental results, the relative energetic stabilities of different overlayer structures have shown some differences with the experimental results. In the GGA calculations, the overlayer structures involving the benzene rings aligned along the (001)-direction were shown to be more stable than those aligned perpendicular to it, regardless of whether the benzoates were arranged in (1x1) or (1x2) symmetries on the (1x1)-unreconstructed surface, or on the (1x2)-reconstructed surface. These are in contrast to the experimental studies using STM, whose observations revealed that configurations with the benzene rings aligned along the (110)-direction when adsorbed on the (1x2)-reconstructed surface.