Charge separation in donor-C60 complexes with real-time Green's functions: The importance of nonlocal correlations

TL;DR

This study demonstrates that nonlocal electronic correlations are crucial for accurately modeling ultrafast charge separation in donor-C60 complexes, revealing that correlation effects enable charge transfer within 10 femtoseconds, unlike mean-field approaches.

Contribution

The paper introduces a real-time Green's function approach to include nonlocal correlations in simulating ultrafast charge dynamics, highlighting their essential role in charge separation processes.

Findings

Charge separation occurs within 10 fs when nonlocal correlations are included.

Mean-field Hartree-Fock fails to predict charge separation, showing near 100% recombination.

Nuclear vibrations have minimal impact unless level misalignment occurs.

Abstract

We use the Nonequilibrium Green's Function (NEGF) method to perform real-time simulations of the ultrafast electron dynamics of photoexcited donor-C60 complexes modeled by a Pariser-Parr-Pople Hamiltonian. The NEGF results are compared to mean-field Hartree-Fock (HF) calculations to disentangle the role of correlations. Initial benchmarking against numerically highly accurate time-dependent Density Matrix Renormalization Group calculations verifies the accuracy of NEGF. We then find that charge-transfer (CT) excitons partially decay into charge separated (CS) states if dynamical non-local correlation corrections are included. This CS process occurs in ~10 fs after photoexcitation. In contrast, the probability of exciton recombination is almost 100% in HF simulations. These results are largely unaffected by nuclear vibrations; the latter become however essential whenever level misalignment hinders the CT process. The robust nature of our findings indicate that ultrafast CS driven by correlation-induced decoherence may occur in many organic nanoscale systems, but it will only be correctly predicted by theoretical treatments that include time-nonlocal correlations.