Before discussing the adsorption of thiols and thiolates on SAMs with ReaxFF, we will shortly summarize experimental and theoretical investigations from the literature regarding the nature of the gold-sulfur bond. Today, a widely accepted theory is that thiol ligands are chemisorbed to the gold surface. During this bond formation, the thiol ligand is expected to convert to its thiolate form, leaving a free hydrogen atom. It is assumed that the hydrogen atoms combine to form H 2 in vacuum, or oxidatively convert into water in the presence of oxygen. On the other hand, the Venkataraman group suggested physisorption of the thiol ligands to the gold surface rather than chemisorption. Their conductance measurements during molecular break junction experiments in solutions revealed that this physisorption occurs without the release of hydrogen. However, they suggested that an excess of ligand molecules in combination with undercoordinated surface atoms again leads to the cleavage of the S-H bond and chemisorption of the ligands. While those high-energy, undercoordinated gold atoms are rare in Au(111) SAMs, the surface of GNPs may be less perfect, especially at the edges of the facets. Hence, undercoordinated gold atoms may be present in GNPs. In combination with an excess of ligands, the formation of thiolates may again be feasible in GNP assemblies.