The nature of two lowest-energy states of Bu symmetry of trans-stilbene and the accurate calculation of their vertical excitation energy have been the subject of a controversy because time dependent density functional theory (TD-DFT) calculations, in agreement with experimental observations, have questioned the results obtained with multireference perturbation theory (MRPT) in the CASPT2 implementation. This paper aims to solve this controversy. By using a different version of MRPT, the n-electron valence state perturbation theory method, the description provided by TD-DFT is confirmed: the lowest Bu singlet state has a HOMO-->LUMO nature and a large oscillator strength (HOMO refers to highest occupied molecular orbital and LUMO refers to lowest unoccupied molecular orbital), while the second Bu singlet state has a mixed HOMO−1-->LUMO and HOMO-->LUMO+1 nature, has an oscillator strength almost vanishing, and is located at 0.6–0.7 eV higher than the first excited state. The computed vertical excitation energy to the first state (3.8–4.0 eV) is in good agreement with the experimental value.
On the controversial nature of the 1 1Bu and 2 1Bu states of trans-stilbene: The n-electron valence state perturbation theory approach.
ANGELI, Celestino;
2009
Abstract
The nature of two lowest-energy states of Bu symmetry of trans-stilbene and the accurate calculation of their vertical excitation energy have been the subject of a controversy because time dependent density functional theory (TD-DFT) calculations, in agreement with experimental observations, have questioned the results obtained with multireference perturbation theory (MRPT) in the CASPT2 implementation. This paper aims to solve this controversy. By using a different version of MRPT, the n-electron valence state perturbation theory method, the description provided by TD-DFT is confirmed: the lowest Bu singlet state has a HOMO-->LUMO nature and a large oscillator strength (HOMO refers to highest occupied molecular orbital and LUMO refers to lowest unoccupied molecular orbital), while the second Bu singlet state has a mixed HOMO−1-->LUMO and HOMO-->LUMO+1 nature, has an oscillator strength almost vanishing, and is located at 0.6–0.7 eV higher than the first excited state. The computed vertical excitation energy to the first state (3.8–4.0 eV) is in good agreement with the experimental value.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
