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Published on: February 15, 2016
Triplet-pair character of the 21Ag dark state of polyenes
Alexandru G Ichert1,2, William Barford1,3
1Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, Oxford, OX1 3QZ, UK.
Abstract:
We define and calculate the triplet-pair population of the 21Ag dark state in polyenes, as predicted by the π-electron Pariser-Parr-Pople (PPP) model, for chains of 8 to 14 C-atoms and Coulomb interaction parameters between 4-14 eV. Our definition of the triplet-pair population is motivated by a two-particle model of the 21Ag state. We use DMRG to solve the PPP model and we exploit the MPS representation of the DMRG wavefunction to compute the triplet-pair population. Using our results for short chain sizes, we predict a finite-size scaling value of the triplet-pair population of ca. 75% for realistic Coulomb interactions for polyene chains. Our results agree with other theoretical work on the doubly-excited character of polyenes, and represent further evidence that the 21Ag state is predominantly triplet-pair in character - with implications for singlet fission mechanisms in polyenes.
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