Abstract: The interaction of additives and ions with the copper surface plays a crucial role in the copper electroplating process. In this work, the interaction of the additives polyethylene glycol (PEG) and bis(3-sulfopropyl)-disulfide (SPS) as well as of chloride with the Cu(111) surface is considered within the framework of density functional theory. In the presence of water, the adsorption energy of chloride diminishes by about 1 eV compared to the case in vacuum. The activation barrier for chloride desorption was found to be 0.8 eV. Simulations of the deposition of copper atoms on a Cl-covered copper surface revealed that Cl atoms are always displaced to the surface. Calculations of adsorption energies of additives in vacuum indicated that the accelerator molecule SPS is bound stronger to Cu(111) than the suppressor molecule PEG. A comparatively strong adsorption of additives was found on a copper surface covered with a Cl–Cu mixed layer. Investigation of the dynamics of additives on Cu(111) by means of first principles molecular dynamics revealed an occasional spontaneous decomposition of an SPS molecule into two MPS molecules. Graphical Abstract: [Figure not available: see fulltext.].