TY - JOUR
T1 - Interface dipoles of organic molecules on Ag(111) in hybrid density-functional theory
AU - Hofmann, Oliver T.
AU - Atalla, Viktor
AU - Moll, Nikolaj
AU - Rinke, Patrick
AU - Scheffler, Matthias
PY - 2013/12/1
Y1 - 2013/12/1
N2 - 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.
AB - 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.
UR - http://www.scopus.com/inward/record.url?scp=84891793869&partnerID=8YFLogxK
U2 - 10.1088/1367-2630/15/12/123028
DO - 10.1088/1367-2630/15/12/123028
M3 - Article
AN - SCOPUS:84891793869
SN - 1367-2630
VL - 15
JO - New Journal of Physics
JF - New Journal of Physics
M1 - 123028
ER -