Excited states of ortho-nitrobenzaldehyde as a challenging case for single- and multi-reference electronic structure theory
© 2023 The Authors. Journal of Computational Chemistry published by Wiley Periodicals LLC.
| Veröffentlicht in: | Journal of computational chemistry. - 1984. - 44(2023), 14 vom: 30. Mai, Seite 1381-1394 |
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| Format: | Online-Aufsatz |
| Sprache: | English |
| Veröffentlicht: |
2023
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| Zugriff auf das übergeordnete Werk: | Journal of computational chemistry |
| Schlagworte: | Journal Article UV/Vis absorption spectroscopy excited states multireference calculations nitro-aromatic compounds single-reference calculations |
| Zusammenfassung: | © 2023 The Authors. Journal of Computational Chemistry published by Wiley Periodicals LLC. We present a large set of vertical excitation calculations for the ortho-nitrobenzaldehyde (oNBA) molecule, which exhibits a very challenging excited-state electronic structure like other nitroaromatic compounds. The single-reference methods produce mostly consistent results up to about 5.5 eV. By contrast, the CAS second-order perturbation theory (CASPT2) results depend sensitively on the employed parameters. At the CAS self-consistent field level, the energies of the bright ππ * states are strongly overestimated while doubly excited states appear too low and mix with these ππ * states. This mixing hampers the CASPT2 step, leading to inconsistent results. Only by increasing the number of states in the state-averaging step to about 40-to cover all bright ππ * states embedded in the double excitations-and employing extended multistate CASPT2 could CASPT2 results consistent with experiment be obtained. We assign the four bands in the molecule's spectrum: The weakest band at 3.7 eV arises from the n NO 2 π * states, the second one at 4.4 eV from the ππ * ( L b ) state, the shoulder at 5.2 eV from the ππ * ( L a ) state, and the maximum at 5.7 eV from the ππ * ( B a / B b ) states. We also highlight the importance of modern wave function analysis techniques in elucidating the absorption spectrum of challenging molecules |
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| Beschreibung: | Date Completed 24.04.2023 Date Revised 24.04.2023 published: Print-Electronic Citation Status PubMed-not-MEDLINE |
| ISSN: | 1096-987X |
| DOI: | 10.1002/jcc.27093 |