Self-Consistent Method for Studying Excitation Energy Transfer in Multichromophoric Systems

Further progress in fundamental understanding of the initial steps of solar-energy conversion in both natural and artificial systems requires computationally inexpensive yet reasonably accurate methods for excited-state quantum dynamics.

Starting from the memory kernel in Born approximation, and recognizing the quantum master equation as the Dyson equation of the Green’s functions theory, we formulate the self-consistent Born approximation (SCBA) to resum the memory-kernel perturbation series in powers of the exciton–environment interaction [1]. Our SCBA is formulated in the Liouville space and frequency domain, and it handles arbitrary spectral densities of the interaction.

In a molecular dimer coupled to an overdamped oscillator environment, we find that the SCBA reproduces the true exciton dynamics very well even in the most challenging regimes of strong interactions, slow environments, and low temperatures. While the SCBA is good (poor) at describing energy transfer modulated by an underdamped vibration resonant (off-resonant) with the exciton energy gap, we find it reasonably describes exciton dynamics in the seven-site model of the Fenna–Matthews–Olson complex in a realistic environment comprising both an overdamped continuum and underdamped vibrations.