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We report the formulation and implementation of an extended Frenkel exciton model (EFEM) designed for simulating the dynamics of multichromophoric systems, taking into account of the possible presence of inter-chromophore charge transfer states, as well as other states in which two chromophores are simultaneously excited. Our approach involves constructing a Hamiltonian based on calculations performed on monomers and selected dimers within the multichromophoric aggregate. The nonadiabatic molecular dynamics is addressed using a surface hopping approach, while the electronic wavefunctions and energies required for constructing the EFEM are computed utilizing the semiempirical floating occupation molecular orbitals-configuration interaction (FOMO-CI) electronic structure method. However, our approach can in principle be adapted to ab initio methods. To validate our method, we simulate the singlet fission process in a trimer of 2,5-bis(fluorene-9 ylidene)-2,5-dihydrothiophene (ThBF) molecules, embedded in their crystal environment, comparing the results of the EFEM to the standard "supermolecule" approach.
Gil et al. (Tue,) studied this question.