Charge transfer via spin flip configuration interaction: Benchmarks and application to singlet fission

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Electronic Structure Theory

Background:

• Characterizing charge transfer and multi-exciton states is challenging for electronic structure theories.
• Restricted active space-spin flip (RAS-SF) methods have been used for multi-exciton states but not charge-transfer states.

Purpose of the Study:

• Introduce a variant of RAS-SF to effectively treat charge-transfer states and electronic couplings.
• Demonstrate the method's utility in analyzing electron transfer mechanisms.

Main Methods:

• Developed a modified RAS-SF approach by partitioning the Hamiltonian into charge-transfer and non-charge-transfer blocks.
• Applied the method to model dimer systems, intramolecular charge-transfer dyads, and a singlet fission system.

Main Results:

• The modified RAS-SF method successfully resolved different types of diabatic states.
• Accurate characterization of charge transfer pathways in donor-acceptor systems was achieved.
• Demonstrated capabilities in analyzing strongly correlated multi-exciton states and electron transfer in singlet fission systems.

Conclusions:

• The proposed RAS-SF variant is a low-cost, accurate tool for studying charge transfer and multi-exciton states.
• Provides valuable insights into electron transfer mechanisms, particularly in complex systems.
• Highlights the method's unique capabilities for advanced electronic structure problems.