Quasiparticle effects on tunneling currents:: A study of C2H4 adsorbed on the Si(001)-(2 x 1) surface

We present a first-principles calculation of the quasiparticlc: electronic structure of ethylene adsorbed on the dimer reconstructed Si(001)-(2 X 1) surface. Within the GW approximation, the self-energy corrections for the adsorbate states are found to be about 1.5 eV larger than those for the states derived from bulk silicon. The calculated quasiparticle band structure is in excellent agreement with photoemission spectra. Finally, the effects of the quasiparticle corrections on the scanning tunneling microscope images of the adsorbed molecules are shown to be important as the lowering of the C2H4 energy levels within GW strongly reduces their tunneling probability.