Scalable Nonmarkovian Exciton Dynamics of Photosynthetic Complexes Using Atomistic Spectral Densities

Samuel Blau, Harvard University

The exciton dynamics of the Fenna-Mathews-Olsen photosynthetic complex (FMO) are modeled using an open quantum systems formalism. We employ an equation of motion with a second-order perturbation in time that explicitly includes nonmarkovian environmental effects. Our bath is assumed to be composed of only harmonic oscillators, and their density of states determines the strength of the system-bath coupling at every frequency. These spectral densities are obtained with atomistic detail from a molecular dynamics simulation. Compressed sensing yields the densities in a basis of Drude-Lorenz peaks and resolves detail more efficiently than a Fourier transform. This facilitates the derivation of an analytical expression for our propagator, allowing for exact evaluation within this framework. The effects of the fine structure of the spectral density are investigated and our model is benchmarked against the more accurate and expensive hierarchical equations of a motion propagator. The results of the two simulations are found to be comparable, but our model can be scaled to much larger systems and higher resolution spectral densities.

Abstract Author(s): Samuel Blau, Thomas Markovich, John Parkhill, Christoph Kreisbeck, Alán Aspuru-Guzik