Hierarchical structures including inorganic and organic constituents allow for excellent mechanical properties found in natural biological composites such as nacre. In order to design new materials mimicking the natural role models, at first, it is essential to understand the involved processes on each hierarchical level. Starting from the smallest relevant length scale this includes the interactions at the interface between inorganic and organic components at the atomistic level. Particularly, carboxylic acids and metal oxides have proven to be excellent choices for the organic and inorganic constituents, respectively .
At the hybrid organic--metal-oxide interface intermolecular forces may contribute to an improved mechanical stability. For instance, linker molecules possessing an aromatic side chain interact with each other via the van-der-Waals interaction.
In this regard, the adsorption of benzoic acids on TiO2 (110) rutile serves as a prototype system. A very regular 2 x 2 overlayer due to dimerization via the phenyl groups has recently been reported .
Here, we present a density functional theory analysis of the dimerization of benzoic acids on TiO2 surfaces. To properly describe the attractive interaction of adsorbing molecules among each other, we applied an exchange correlation functional with van-der-Waals correction. For all surface orientations, the preferred dimer formation mode (hydrogen - to - ? - orbital or tilted and twisted ? - to - ?) as well as the amount of energy gain resulting from dimerization will be discussed.
 Dreyer et al., Nature Mater. (2016) 10.1038/nmat4553.
 Grinter et al., J. Phys. Chem. Lett. 5, 4265 (2014).