Lateral adsorption geometry and site-specific electronic structure of a large organic chemisorbate on a metal surface

A combined study of scanning tunneling microscopy (STM) and density functional theory (DFT) reveals that 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) adsorbs on Ag(111) at bridge sites in two nonequivalent orientations, one nearly aligned with the [10 (1) over bar] substrate axis and the other 18 degrees misaligned. Site-specific spectroscopy reveals that molecules in the two configurations exhibit subtle differences in their electronic structure. DFT-based STM simulations trace these back to the influence of distinct local adsorption geometries on the chemical molecule-substrate and molecule-molecule interactions.