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Puschnig P, Boese AD, Willenbockel M, Meyer M, Lüftner D, Reinisch EM, Ules T, Koller G, Soubatch S, Ramsey MG, Tautz FS. Energy Ordering of Molecular Orbitals. J Phys Chem Lett 2017; 8:208-213. [PMID: 27935313 PMCID: PMC5220489 DOI: 10.1021/acs.jpclett.6b02517] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2016] [Accepted: 12/09/2016] [Indexed: 05/17/2023]
Abstract
Orbitals are invaluable in providing a model of bonding in molecules or between molecules and surfaces. Most present-day methods in computational chemistry begin by calculating the molecular orbitals of the system. To what extent have these mathematical objects analogues in the real world? To shed light on this intriguing question, we employ a photoemission tomography study on monolayers of 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA) grown on three Ag surfaces. The characteristic photoelectron angular distribution enables us to assign individual molecular orbitals to the emission features. When comparing the resulting energy positions to density functional calculations, we observe deviations in the energy ordering. By performing complete active space calculations (CASSCF), we can explain the experimentally observed orbital ordering, suggesting the importance of static electron correlation beyond a (semi)local approximation. On the other hand, our results also show reality and robustness of the orbital concept, thereby making molecular orbitals accessible to experimental observations.
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Affiliation(s)
- P. Puschnig
- Institute
of Physics, University of Graz, NAWI-Graz, Universitätsplatz
5, 8010 Graz, Austria
- E-mail:
| | - A. D. Boese
- Institute
of Chemistry, University of Graz, NAWI Graz, Heinrichstraße 28/IV, 8010 Graz, Austria
| | - M. Willenbockel
- Peter
Grünberg Institut (PGI-3), Forschungszentrum
Jülich, 52425 Jülich, Germany
- Jülich
Aachen
Research Alliance (JARA), Fundamentals of Future Information Technology, 52425 Jülich, Germany
| | - M. Meyer
- Peter
Grünberg Institut (PGI-3), Forschungszentrum
Jülich, 52425 Jülich, Germany
- Jülich
Aachen
Research Alliance (JARA), Fundamentals of Future Information Technology, 52425 Jülich, Germany
| | - D. Lüftner
- Institute
of Physics, University of Graz, NAWI-Graz, Universitätsplatz
5, 8010 Graz, Austria
| | - E. M. Reinisch
- Institute
of Physics, University of Graz, NAWI-Graz, Universitätsplatz
5, 8010 Graz, Austria
| | - T. Ules
- Institute
of Physics, University of Graz, NAWI-Graz, Universitätsplatz
5, 8010 Graz, Austria
| | - G. Koller
- Institute
of Physics, University of Graz, NAWI-Graz, Universitätsplatz
5, 8010 Graz, Austria
| | - S. Soubatch
- Peter
Grünberg Institut (PGI-3), Forschungszentrum
Jülich, 52425 Jülich, Germany
- Jülich
Aachen
Research Alliance (JARA), Fundamentals of Future Information Technology, 52425 Jülich, Germany
| | - M. G. Ramsey
- Institute
of Physics, University of Graz, NAWI-Graz, Universitätsplatz
5, 8010 Graz, Austria
| | - F. S. Tautz
- Peter
Grünberg Institut (PGI-3), Forschungszentrum
Jülich, 52425 Jülich, Germany
- Jülich
Aachen
Research Alliance (JARA), Fundamentals of Future Information Technology, 52425 Jülich, Germany
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