Coronene . Adatom defects have a considerable impact on the adsorption of PAHs. On a pristine surface, [6]C binds more strongly than either of the [6]H enantiomers. Its planarity and extended conjugation maximize dispersive molecule-surface interactions for [6]C, whereas non-planar helicene molecules experience weaker binding, despite extended conjugation, two additional carbon atoms, and a footprint similar to that of [6]C (see Table for binding energies, consistent with previous work ). The strong interaction on pristine surfaces is reflected in the major impact of surface binding on the carbon-atom PDOS for [6]C. In the top panel of Figure (c), the carbon-atom states shown in blue for gas phase [6]C shift to significantly lower energies and broaden in the adsorbed phase (cyan line).