All-Mode Quantum-Classical Path Integral Simulation of Bacteriochlorophyll Dimer Exciton-Vibration Dynamics

Area of Science:

• Quantum dynamics
• Photosynthetic light-harvesting complexes
• Biophysics

Background:

• Bacteriochlorophyll dimers are crucial light-harvesting components in photosynthesis.
• Understanding exciton-vibration dynamics is key to elucidating energy transfer efficiency.
• Previous models often simplified the complex vibrational environment.

Purpose of the Study:

• To perform numerically exact quantum mechanical simulations of exciton-vibration dynamics.
• To explicitly include all vibrational modes in the bacteriochlorophyll dimer system.
• To investigate the impact of initial conditions and static disorder on dynamics.

Main Methods:

• Quantum-classical path integral (QCPI) methodology for fully quantum mechanical calculations.
• Coordinate transformation to a spin-Boson Hamiltonian with a collective bath.
• Inclusion of 50 coupled vibrational normal modes per bacteriochlorophyll, parameterized by Huang-Rhys factors.

Main Results:

• Demonstrated persistent, underdamped oscillations of electronic energy between pigments at room temperature.
• Observed that static disorder introduces damping but preserves oscillatory population dynamics.
• Identified atypical, nonsmooth features in population curves due to complex vibrational spectra, unresolvable by simple spectral densities.

Conclusions:

• The study provides a highly accurate, quantum mechanical picture of exciton-vibration dynamics in bacteriochlorophyll dimers.
• Complex vibrational spectra significantly influence energy transfer dynamics, necessitating detailed modeling.
• The findings highlight the importance of including the full vibrational manifold for accurate biophysical simulations.