Multi-Layer Multi-Configuration Time-Dependent Hartree (ML-MCTDH) Approach to the Correlated Exciton-Vibrational Dynamics in the FMO Complex

TL;DR

This paper applies the ML-MCTDH method to simulate high-dimensional exciton-vibrational dynamics in the FMO complex, revealing insights into energy transfer pathways and the influence of initial excitation conditions.

Contribution

It introduces a multi-layer MCTDH approach to model complex exciton-vibrational interactions in large FMO systems with detailed vibrational mode coupling.

Findings

Vibrational and vibronic excitations significantly influence energy transfer pathways.

Distinct time scales of vibrational and exciton motions affect dynamics.

Initial state preparation impacts excitation energy flow.

Abstract

The coupled quantum dynamics of excitonic and vibrational degrees of freedom is investigated for high-dimensional models of the Fenna-Matthews-Olson (FMO) complex. This includes a seven and an eight-site model with 518 and 592 harmonic vibrational modes, respectively. The coupling between local electronic transitions and vibrations is described within the Huang-Rhys model using parameters that are obtained by discretization of an experimental spectral density. Different pathways of excitation energy flow are analyzed in terms of the reduced one-exciton density matrix, focussing on the role of vibrational and vibronic excitation. Distinct features due to both competing time scales of vibrational and exciton motion and vibronically-assisted transfer are observed. The question of the effect of initial state preparation is addressed by comparing the case of an instantaneous Franck-Condon excitation at a single site with that of a laser field excitation.