The electronic transport properties of molecular junctions are very sensitive to the contact configuration which is usually not very well known. One type of setup which allows more control over the contact geometry uses an STM (scanning tunnelling microscope) tip as one of the electrodes enabling the investigation of both the electronic and geometric structure of the junction. We present, using the nonequilibrium Green function formalism in combination with DFT [2-4], the results of our recent calculations related to a set of experiments studying PTCDA on metallic surfaces [1]. The calculations allow for the systematic investigation of the effect of the contact geometry on the transport properties of molecular junctions, which should in turn improve the agreement between theory and experiment.

[1] R. Temirov, A. Lassise, F. B. Anders, and F. S. Tautz, Nanotechnology 19, 065401 (2008).
[2]F. Pump et al., Appl. Phys. A 93, 335 (2008).
[3] A. R. Rocha et al., Phys. Rev. B 73, 085414 (2006).
[4] A. Pecchia and A. Di Carlo, Rep. Prog. Phys. 67, 1497 (2004).