An ab initio exciton model for singlet fission

Area of Science:

• Computational Chemistry
• Materials Science
• Photophysics

Background:

• Singlet fission is a crucial photophysical process for enhancing solar cell efficiency.
• Existing models often require parameterization or struggle with computational scalability for complex systems.

Purpose of the Study:

• To develop a general, parameter-free, and computationally efficient exciton model for simulating singlet fission.
• To accurately predict excited states, energies, and couplings in multichromophoric systems.

Main Methods:

• An ab initio exciton model extending the Frenkel exciton model.
• Inclusion of valence, charge-transfer, and multiexcitonic excited states.
• Validation against multiconfigurational methods for pentacene dimer.

Main Results:

• The model accurately predicts energies and couplings for the pentacene dimer.
• Demonstrated computational scalability for larger pentacene clusters.
• Identified mixing of local and charge-transfer excitations narrowing the singlet-multiexcitonic gap.
• Found that local vibrations facilitate singlet-multiexcitonic state-crossing.

Conclusions:

• The developed exciton model provides a robust and scalable approach for singlet fission simulations.
• The model captures key physical aspects, including the role of charge-transfer states and molecular vibrations.
• This work lays the foundation for first-principles nonadiabatic quantum molecular dynamics simulations of singlet fission.