Electron delocalization at the hybrid aromatic-thiol/Cu(100) interface

We present an in-depth investigation of the structural and electronic properties of a p(2x2) mercaptobenzoxazole (MBO) monolayer on the Cu(100) surface by means of repeated supercell density functional theory simulations. Our results show that the formation of the interface, with the molecular S headgroups lying at four-fold coordination sites on the metal substrate, is a strongly exothermic reaction that brings an energy gain of 1.4 eV/molecule with respect to the free surface and gas-phase thione molecules. The electronic structure of the most stable atomic configuration is characterized by bonding and antibonding hybrid metal-molecule electron states obtained from coupling between the p orbitals of the S atoms and the d orbitals of the Cu atoms. A detailed assignment of the experimental photoemission peaks, which were revealed by recent measurements, can be traced on the basis of our computational findings. In addition, we are able to show that the deposition of MBO on Cu(100) results in chemisorption rather than physisorption and to fix the relative position of the metal Fermi level with respect to the molecular levels of the highest occupied and lowest unoccupied molecular orbitals.