The nature of the chemical bonding of a pentacene molecule to a gold surface was studied. The calculations were carried out using two very different methodologies, the ab inito gaussian molecular orbital method and a numerical atomic orbital method. To within computational and experimental error, it was found that the best description of the binding energies could be obtained using GAUSSIAN calculations using long-range ωB97 and ωB97X exchange functionals. Thus the nature of chemical bonding of pentacene to gold was of van der Waals type. To understand the large variation in the geometries computed by different methods, energy profiles were calculated in both the X- and Y-directions. The energy barriers appeared to be very small and comparable to the value at room temperature. Thus a pentacene molecule moved on a gold surface with almost no friction at room temperature. An estimation of the work function was often obtained from a simple electrostatic approach. This estimation was tested and it was found that this approach could not be used because it significantly underestimated the work function. This investigation furnished insights into the structure and bonding of pentacene to a gold surface and provided ideas for the improvement of methodologies for computing the properties of van der Waals adsorbates.

The Adsorption Energy and Diffusion of a Pentacene Molecule on a Gold Surface. W.D.Wheeler, B.A.Parkinson, Y.Dahnovsky: Journal of Chemical Physics, 2011, 135[2], 024702