Adsorption structure and scanning tunneling data of a prototype organic-inorganic interface: PTCDA on Ag(111)

We present density-functional calculations of a monolayer of 3,4,9,10-perylene-tetracarboxylic-dianhydride adsorbed on the Ag(111) surface, yielding detailed insight into the structural and electronic properties of this prototypical adsorption system. Using the local-density approximation as the best choice for the exchange-correlation functional, we discuss the bond lengths inside the molecules, the distortion of the molecules due to adsorption, and their position and orientation relative to the substrate and to each other. Based on the calculated geometric and electronic structures, we calculate scanning tunneling microscopy and spectroscopy data within the Tersoff-Hamann framework [Phys. Rev. B. 31, 805 (1985)]. To this end, two-dimensional Fourier transform methods and spatial extrapolation techniques are employed to evaluate the sample wave functions at the tip position. We obtain constant-current images and spectral data that reveal detailed information about the electronic structure of the system. In addition, we have measured the same data by low-temperature scanning tunneling microscopy and scanning tunneling spectroscopy. Our measured and calculated data are in good agreement with one another.