Multiscale QM/MM molecular dynamics simulations of the trimeric major light-harvesting complex II

Area of Science:

• Photosynthesis research
• Computational biophysics
• Quantum chemistry

Background:

• Photosynthesis relies on sunlight, but excess light can damage cellular machinery.
• Light-Harvesting Complex (LHCII) in plants manages light absorption and energy dissipation (quenching).
• Understanding exciton dynamics and quenching requires accurate spectral density determination.

Purpose of the Study:

• To accurately simulate the spectral density of the LHCII complex.
• To investigate exciton dynamics and light-harvesting/quenching balance.
• To validate a novel multi-scale computational scheme against experimental data.

Main Methods:

• Employed Born-Oppenheimer molecular dynamics simulations with a quantum mechanics/molecular mechanics (QM/MM) approach.
• Utilized the density functional based tight binding (DFTB) method for ground and excited state calculations.
• Applied a time-dependent extension of the long-range-corrected DFTB scheme for excited states.

Main Results:

• Successfully simulated spectral densities for the LHCII complex with high accuracy.
• Achieved excellent agreement between simulated spectral densities and experimental data.
• Calculated exciton transfer rates in a chlorophyll-a/carotenoid pigment pair.

Conclusions:

• The multi-scale QM/MM-DFTB scheme is accurate, robust, and reliable for large biological systems.
• This study represents the first theoretical simulation of spectral density for such a large complex.
• The findings provide insights into the balance of light harvesting and photoprotective quenching mechanisms.