Ab initio study of benzene adsorption on the Cu(1 1 0) surface and simulation of STM images

Abstract

The adsorption of benzene molecules onto the Cu(110) surface has been studied using a crystalline linear combination of atomic orbitals approximation (LCAO). Adsorption energetics have been modeled at both the Hartree-Fock (HF) and density functional theory (DFT) level, and scanning tunneling microscope (STM) images generated for the preferred adsorption geometry. The calculated binding energies are strongly dependent upon basis set superposition errors (BSSE). As expected HF provides a relatively poor description of this loosely bound system, and is found to be unbound when BSSE is taken into account. Inclusion of electron correlation through DFT methods gives an optimized binding energy of 106 kJ mol-1 with the benzene molecule occupying a bridging site between the rows of surface copper atoms and an adsorption height of approximately 2 Å. This figure takes account of relaxation of benzene upon absorption with the hydrogen atoms tilting away from the surface. Our predicted energetics compare favourably with previous theoretical studies using cluster methods and experimental binding energies determined from temperature programmed desorption (TPD). We have also simulated scanning tunneling microscope (STM) images using the Tersoff and Hamann method and compare our results with recent experimental measurements. Our simulation suggests the experimental image results from a benzene dimer rather than an isolated molecule.