Nicolas P. D. Sawaya ^*†, Joonsuk Huh ^*†, Takatoshi Fujita ^†, Semion K. Saikin ^†‡, and Alan Aspuru-Guzik ^*†

^† Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138, United States
^‡ Institute of Physics, Kazan Federal University, 18 Kremlevskaya Street, Kazan 420008, Russian  Federation

^*Correspondence to Nicolas P. D. Sawaya, Joonsuk Huh, Alan Aspuru-Guzik

ABSTRACT
Chlorosomes are efficient light-harvesting antennas containing up to hundreds of thousands of bacteriochlorophyll molecules. With massively parallel computer hardware, we use a nonperturbative stochastic Schrödinger equation, while including an atomistically derived spectral density, to study excitonic energy transfer in a realistically sized chlorosome model. We find that fast short-range delocalization leads to robust long-range transfer due to the antennae’s concentric-roll structure. Additionally, we discover anomalous behavior arising from different initial conditions, and outline general considerations for simulating excitonic systems on the nanometer to micrometer scale.

KEYWORDS: Chlorosome, photosynthesis, green sulfur bacteria, exciton, spectral density, graphics processing unit