First-Principles Models for Biological Light-Harvesting: Phycobiliprotein Complexes from Cryptophyte Algae.

Area of Science:

• Quantum mechanics
• Spectroscopy
• Biophysics

Background:

• Photosynthetic light harvesting relies on efficient energy transfer.
• The Frenkel exciton model is widely used but faces parametrization challenges.
• Unique and interpretable model parameters are crucial for understanding energy transfer.

Purpose of the Study:

• To develop a computational approach for unique and physically interpretable model Hamiltonian parametrization.
• To capture fluctuations in light harvesting systems using an ensemble of local models.
• To apply the method to phycobiliprotein light harvesting complexes.

Main Methods:

• Utilizing first-principles electronic structure methods.
• Employing molecular dynamics and QM geometry optimization to sample local minima.
• Constructing a Hamiltonian ensemble to describe system fluctuations.
• Applying non-Markovian reduced density matrix dynamics for spectral line shape analysis.

Main Results:

• The developed approach provides a reliable, first-principles method for computing spectra.
• The Hamiltonian ensemble captures inhomogeneous broadening and electronic-vibrational coupling.
• The method successfully distinguishes the influence of different chromophore protonation states.
• It accurately describes intrachromophore vibrations during excitation and energy transfer.

Conclusions:

• The computational approach offers a robust method for parametrizing model Hamiltonians in light harvesting systems.
• This work provides a first-principles understanding of spectral properties and energy transfer dynamics.
• The findings are validated by experimental results from cryptophyte algae phycobiliproteins.