TY  - JOUR
AU  - Puschnig, P.
AU  - Boese, A. D.
AU  - Willenbockel, M.
AU  - Meyer, M.
AU  - Lüftner, D.
AU  - Reinisch, E. M.
AU  - Ules, T.
AU  - Koller, G.
AU  - Soubatch, S.
AU  - Ramsey, M. G.
AU  - Tautz, F. S.
TI  - Energy Ordering of Molecular Orbitals
JO  - The journal of physical chemistry letters
VL  - 8
IS  - 1
SN  - 1948-7185
CY  - Washington, DC
PB  - ACS
M1  - FZJ-2017-00323
SP  - 208 - 213
PY  - 2016
AB  - 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.
LB  - PUB:(DE-HGF)16
UR  - <Go to ISI:>//WOS:000391653200032
C6  - pmid:27935313
DO  - DOI:10.1021/acs.jpclett.6b02517
UR  - https://juser.fz-juelich.de/record/826054
ER  -