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

Abstract

We investigate the molecular acceptors 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA), 2, 3,5,7,8, 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.

Electronic charge rearrangement at metal/organic interfaces induced by weak van der Waals interactions

“…Tuning the electronic properties of HMOS is an outstanding challenge, investigated both theoretically [13,[16][17][18][19] and experimentally [20][21][22][23]. For example, the shift of the metal work function upon molecular adsorption, one of the most important properties of HMOS, can be achieved by three distinct effects: (i) the Pauli pushback, i.e., the repulsion between the electrons belonging to the metal surface and those of the adsorbed molecules; (ii) the presence of a charge transfer between the surface and the monolayer; (iii) the intrinsic electronic dipole of the monolayer.…”

Atomic-Level Structural and Electronic Properties of Hybrid Inorganic–Organic ZnO:Hydroquinone Superlattices Fabricated by ALD/MLD

“…Hybrid density functional methods have been recently benchmarked and successfully applied in several computational investigations on hybrid ZnO/organic materials and interfaces. [35][36][37][38] We derived explicit atomistic structural models for the ZnO:HQ superlattices starting from bulk ZnO. Bulk ZnO crystallizes in the hexagonal wurtzite structure with four atoms in the primitive cell (space group P6 3 mc).…”

Interplay of local and global interfacial electronic structure of a strongly coupled dipolar organic semiconductor

“…All observed attributes of the state labeled "f-LUMO" suggest strongly that this state is formed by partial electron transfer from Cu(111) to a previously unoccupied state of the molecule: i) The peak center is very close to E F , with E F bisecting the peak; ii) assignment of this feature as HOMO is incompatible with an ionization energy of approximately 6 eV reported previously on Ag(111) [31] and measured by us on graphite, given a global work function below 4.5 eV; iii) the solution HOMO-LUMO gap of ~2.2 eV [40] predicts to first approximation a LUMO energy near E F ; iv) the localized, non-dispersive electronic character is indicative of a molecular level; and v) the disappearance of this peak at coverages r 1 MLE is expected for an interface-specific feature arising from charge-transfer from the surface to a molecule. Given this interpretation of the "f-LUMO", the binding energy of -0.03(2) eV at k || = 0 implies transfer of close to a full electron to the molecule and is presumably accompanied by backdonation to lower lying molecular orbitals [41].…”