The open–access journal for physics New Journal of Physics Theoretical study of PTCDA adsorbed on the coinage metal surfaces, Ag(111), Au(111) and Cu(111) L Romaner 1,2,3 , D Nabok 1 , P Puschnig 1 , E Zojer 2 and C Ambrosch-Draxl 1 1 Chair of Atomistic Modelling and Design of Materials, University of Leoben, Franz-Josef-Straße 18, A-8700 Leoben, Austria 2 Institute of Solid State Physics, Graz University of Technology, Petersgasse 16, A-8010 Graz, Austria E-mail: lorenz.romaner@unileoben.ac.at New Journal of Physics 11 (2009) 053010 (21pp) Received 11 February 2009 Published 22 May 2009 Online at http://www.njp.org/ doi:10.1088/1367-2630/11/5/053010 Abstract. A thorough understanding of the adsorption of molecules on metallic surfaces is a crucial prerequisite for the development and improvement of functionalized materials. A prominent representative within the class of π -conjugated molecules is 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA) which, adsorbed on the Ag(111), Au(111) or Cu(111) surfaces, shows characteristic trends for work-function modification, alignment of molecular levels with the substrate Fermi energy and binding distances. We carried out density functional theory (DFT) calculations to investigate to what extent these trends can be rationalized on a theoretical basis. We used different density functionals (DF) including a fully non-local van der Waals (vdW) DF capable of describing dispersion interactions. We show that, rather independent of the DF, the calculations yield level alignments and work-function modifications consistent with ultra-violet photoelectron spectroscopy when the monolayer is placed onto the surfaces at the experimental distances (as determined from x- ray standing wave experiments). The lowest unoccupied molecular orbital is occupied on the Ag and Cu surfaces, whereas it remains unoccupied on the Au surface. Simultaneously, the work function increases for Ag but decreases for Cu and Au. Adsorption distances and energies, on the other hand, depend very sensitively on the choice of the DF. While calculations in the local density approximation bind the monolayer consistently with the experimental trends, the generalized gradient approximation in several flavors fails to reproduce 3 Author to whom any correspondence should be addressed. New Journal of Physics 11 (2009) 053010 1367-2630/09/053010+21$30.00 © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft