  By means of quasiparticle-energy calculations in the G0W0 approach, we show
for the prototypical insulator/semiconductor system NaCl/Ge(001) that
polarization effects at the interfaces noticeably affect the excitation
spectrum of molecules adsorbed on the surface of the NaCl films. The magnitude
of the effect can be controlled by varying the thickness of the film, offering
new opportunities for tuning electronic excitations in e.g. molecular
electronics or quantum transport. Polarization effects are visible even for the
excitation spectrum of the NaCl films themselves, which has important
implications for the interpretation of surface science experiments for the
characterization of insulator surfaces.
