Experimental and theoretical electronic structure of quinacridone

Daniel Lüftner, Sivan Refaely-Abramson, Michael Pachler, Roland Resel, Michael G. Ramsey, Leeor Kronik, and Peter Puschnig
Phys. Rev. B 90, 075204 – Published 25 August 2014

Abstract

The energy positions of frontier orbitals in organic electronic materials are often studied experimentally by (inverse) photoemission spectroscopy and theoretically within density functional theory. However, standard exchange-correlation functionals often result in too small fundamental gaps, may lead to wrong orbital energy ordering, and do not capture polarization-induced gap renormalization. Here we examine these issues and a strategy for overcoming them by studying the gas phase and bulk electronic structure of the organic molecule quinacridone (5Q), a promising material with many interesting properties for organic devices. Experimentally we perform angle-resolved photoemission spectroscopy (ARUPS) on thin films of the crystalline β phase of 5Q. Theoretically we employ an optimally tuned range-separated hybrid functional (OT-RSH) within density functional theory. For the gas phase molecule, our OT-RSH result for the ionization potential (IP) represents a substantial improvement over the semilocal PBE and the PBE0 hybrid functional results, producing an IP in quantitative agreement with experiment. For the bulk crystal we take into account the correct screening in the bulk, using the recently developed optimally tuned screened range-separated hybrid (OT-SRSH) approach, while retaining the optimally tuned parameters for the range separation and the short-range Fock exchange. This leads to a band gap narrowing due to polarization effects and results in a valence band spectrum in excellent agreement with experimental ARUPS data, with respect to both peak positions and heights. Finally, full-frequency G0W0 results based on a hybrid functional starting point are shown to agree with the OT-SRSH approach, improving substantially on the PBE-starting point.

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  • Received 7 July 2014
  • Revised 11 August 2014

DOI:https://doi.org/10.1103/PhysRevB.90.075204

©2014 American Physical Society

Authors & Affiliations

Daniel Lüftner1, Sivan Refaely-Abramson2, Michael Pachler1,3, Roland Resel3, Michael G. Ramsey1, Leeor Kronik2, and Peter Puschnig1,*

  • 1Institute of Physics, University of Graz, NAWI Graz, Universitätsplatz 5, 8010 Graz, Austria
  • 2Department of Materials and Interfaces, Weizmann Institute of Science, Rehovoth 76100, Israel
  • 3Institute of Solid State Physics, Graz University of Technology, NAWI Graz, Petersgasse 16, 8010 Graz, Austria

  • *peter.puschnig@uni-graz.at

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Vol. 90, Iss. 7 — 15 August 2014

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