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Interface dipoles of organic molecules on Ag(111) in hybrid density-functional theory

MPS-Authors
http://pubman.mpdl.mpg.de/cone/persons/resource/persons21637

Hofmann,  Oliver T.
Theory, Fritz Haber Institute, Max Planck Society;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons21311

Atalla,  Viktor
Theory, Fritz Haber Institute, Max Planck Society;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons22010

Rinke,  Patrick
Theory, Fritz Haber Institute, Max Planck Society;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons22064

Scheffler,  Matthias
Theory, Fritz Haber Institute, Max Planck Society;

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1367-2630_15_12_123028.pdf
(Publisher version), 3MB

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Citation

Hofmann, O. T., Atalla, V., Moll, N., Rinke, P., & Scheffler, M. (2013). Interface dipoles of organic molecules on Ag(111) in hybrid density-functional theory. New Journal of Physics, 15(12): 123028. doi:10.1088/1367-2630/15/12/123028.


Cite as: http://hdl.handle.net/11858/00-001M-0000-0014-D156-9
Abstract
We investigate the molecular acceptors 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA), 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) and 4,5,9,10-pyrenetetraone (PYTON) on Ag(111) using density-functional theory (DFT). For two groups of the Heyd–Scuseria–Ernzerhof (HSE(α, ω)) family of exchange-correlation functionals (ω = 0 and 0.2 Å) we study the isolated components as well as the combined systems as a function of the amount of exact-exchange (α). We find that hybrid functionals favour electron transfer to the adsorbate. Comparing with experimental work function data, for α ≈ 0.25 we report a notable but small improvement over (semi) local functionals for the interface dipole. Although Kohn–Sham eigenvalues are only approximate representations of ionization energies, incidentally, at this value also the density of states agrees well with the photoelectron spectra. However, increasing α to values for which the energy of the lowest unoccupied molecular orbital matches the experimental electron affinity in the gas phase worsens both the interface dipole and the density of states. Our results imply that semi-local DFT calculations may often be adequate for conjugated organic molecules on metal surfaces and that the much more computationally demanding hybrid functionals yield only small improvements.