Time-Dependent Atomistic Simulations of the CP29 Light-Harvesting Complex

TL;DR

This paper presents a novel computational approach combining DFTB and QM/MM methods to determine spectral densities and study excitation energy transfer in the CP29 light-harvesting complex, enhancing understanding of photosynthetic processes.

Contribution

It introduces a time-dependent atomistic simulation framework for spectral densities in CP29, integrating DFTB with QM/MM and wave packet dynamics for the first time.

Findings

Spectral densities vary with different force fields.

Comparison with other complexes shows unique spectral features.

Excitation energy transfer dynamics are characterized in detail.

Abstract

Light harvesting as the first step in photosynthesis is of prime importance for life on earth. For a theoretical description of photochemical processes during light harvesting, spectral densities are key quantities. They serve as input functions for modeling the excitation energy transfer dynamics and spectroscopic properties. Herein, a recently developed procedure is applied to determine the spectral densities of the pigments in the minor antenna complex CP29 of photosystem II which has recently gained attention because of its active role in non-photochemical quenching processes in higher plants. To this end, the density functional based tight binding (DFTB) method has been employed to enable simulation of the ground state dynamics in a quantum-mechanics/molecular mechanics (QM/MM) scheme for each chlorophyll pigment. Subsequently, the time-dependent extension of the long-range corrected DFTB approach has been used to obtain the excitation energy fluctuations along the ground-state trajectories also in a QM/MM setting. From these results the spectral densities have been determined and compared for different force fields and to spectral densities from other light-harvesting complexes. In addition, the excitation energy transfer in the CP29 complex has been studied using ensemble-average wave packet dynamics.