Charge Separation in Donor-C₆₀ Complexes with Real-Time Green Functions: The Importance of Nonlocal Correlations

Area of Science:

• Computational Chemistry
• Quantum Dynamics
• Materials Science

Background:

• Understanding ultrafast electron dynamics is crucial for designing organic electronic devices.
• Donor-C60 complexes are model systems for studying charge transfer processes.
• Accurate theoretical methods are needed to capture correlation effects in excited states.

Purpose of the Study:

• To investigate the role of electron correlations in the ultrafast dynamics of photoexcited donor-C60 complexes.
• To compare the nonequilibrium Green function (NEGF) method with Hartree-Fock (HF) calculations.
• To elucidate the mechanisms of exciton decay and charge separation.

Main Methods:

• Real-time simulations using the nonequilibrium Green function (NEGF) method.
• Modeling donor-C60 complexes with the Pariser-Parr-Pople Hamiltonian.
• Benchmarking NEGF against time-dependent density matrix renormalization group (TDDMRG) calculations.
• Comparison with mean-field Hartree-Fock (HF) simulations.

Main Results:

• NEGF accurately predicts electron dynamics, verified by TDDMRG.
• Dynamical nonlocal correlations drive partial decay of charge-transfer (CT) excitons into charge-separated (CS) states within ~10 fs.
• HF simulations show near-complete exciton recombination, neglecting crucial correlation effects.
• Nuclear vibrations have a minor impact unless level misalignment impedes CT.

Conclusions:

• Ultrafast charge separation driven by correlation-induced decoherence is significant in organic nanoscale systems.
• Theoretical methods incorporating time-nonlocal correlations are essential for accurate predictions.
• The NEGF method provides a reliable framework for studying these complex dynamics.