Electronic states of adsorbed organic molecule: Pentacene on Si(001)2x1 surface

Electronic states are calculated by the DV-X alpha-LCAO method for four model clusters of the pentacene molecule adsorbed on dimer rows of the Si(001)2 x 1 surface. About 2 electrons transfer from the Si substrate to pentacene molecule. These electrons are loosely localized in the region of the pentacene molecule above the Si dimers. The calculated charge dencities of individual occupied and unoccupied orbitals near the Fermi level are compared with the scanning tunneling microscopy (STM) images. The good reproducibility of the STM images implies that electrons tunnel from/to the eigenstates of the combined system of the adsorbed organic molecule and the Si substrate where the adsorbate molecule is assumed to bond covalently to dangling bonds of Si dimers.