Nonorthogonal Multireference Wave Function Description of Triplet–Triplet Energy Transfer Couplings

Abstract

In this study, the use of self-consistent field quasi-diabats is investigated for calculation of triplet energy transfer diabatic coupling elements. It is proposed that self-consistent field quasi-diabats are particularly useful for studying energy transfer (EnT) processes because orbital relaxation in response to changes in electron configuration is implicitly built into the model. The conceptual model that is developed allows for the simultaneous evaluation of direct and charge-transfer mechanisms to establish the importance of the different possible EnT mechanisms. The method’s performance is evaluated using two model systems: the ethylene dimer and ethylene with the methaniminium cation. While states that mediate the charge-transfer mechanism were found to be higher in energy than the states involved in the direct mechanism, the coupling elements that control the kinetics were found to be significantly larger in the charge-transfer mechanism. Subsequently, we discuss the advantage of the approach in the context of practical difficulties with the use of established approaches.

Triplet Excitation-Energy Transfer Couplings from Subsystem Time-Dependent Density-Functional Theory

“…In the context of one-particle and two-particle coupling interactions, Beratan and co-workers have proposed a much simpler and more intuitive approach to describing TEET couplings by predicting TEET interactions from molecular orbital (MO) overlaps with respect to direct and bridge-mediated donor–acceptor couplings . Thompson et al recently employed quasi-diabatic self-consistent field (SCF) solutions to compute TEET couplings …”