The Role of Hydrogen Bonding and Proton Transfer in the Formation of Uracil Networks on the Gold (100) Surface: A Density Functional Theory Approach

We have used density functional theory calculations, including a correction for the dispersive forces (DFT-D), to investigate the formation of a monolayer superstructure of uracil molecules adsorbed on the Au(100) surface. Our calculations provide insight into the interplay between lateral adsorbate adsorbate and vertical adsorbate substrate interactions, where we found that uracil adsorption to the surface is strongly dependent on the lateral interactions, particularly hydrogen bonding, although the first adsorbed molecule, before the formation of a uracil network, is covalently bonded to the surface. The self-assembly of the uracil network on the surface is mediated by proton transfer, and the ensuing charge separation stabilizes the geometry. Dispersive forces also play a role, and in particular, the introduction of a correction leads to flatter geometries with molecules lying parallel to the surface, thereby enhancing pi-pi stacking and hydrogen-bonding.