Long-time quantum simulation of the primary charge separation in bacterial photosynthesis.

248

415

Singlet fission, a spin-allowed energy transfer process generating two triplet excitons from one singlet exciton, has the potential to dramatically increase the efficiency of organic solar cells. However, the dynamical mechanism of this phenomenon is not fully understood and a complete, microscopic theory of singlet fission is lacking. In this work, we assemble the components of a comprehensive microscopic theory of singlet fission that connects excited state quantum chemistry calculations with finite-temperature quantum relaxation theory. We elaborate on the distinction between localized diabatic and delocalized adiabatic bases for the interpretation of singlet fission experiments in both the time and frequency domains. We discuss various approximations to the exact density matrix dynamics and propose Redfield theory as an ideal compromise between speed and accuracy for the detailed investigation of singlet fission in dimers, clusters, and crystals. Investigations of small model systems based on parameters typical of singlet fission demonstrate the numerical accuracy and practical utility of this approach.

Section: A Results For Population Dynamicsmentioning

confidence: 99%

Section: A Results For Population Dynamicsmentioning

confidence: 99%

Microscopic theory of singlet exciton fission. I. General formulation

Berkelbach¹,

Hybertsen²,

Reichman³

2013

248

415

“…In these experiments the primary electron donor (the special pair) is chemically oxidized, shutting down the electron transfer 43 so that only excited state energy transfer between the accessory bacteriochlorophyll (Bchl or B) and bacteriopheophytin (BPhy, or H) is possible. The 2D photon echo experiments by Lee et al 1 showed a long lived beating signal associated with |H B| coherent dynamics.…”

Section: Model Systemsmentioning

confidence: 99%

Influence of environment induced correlated fluctuations in electronic coupling on coherent excitation energy transfer dynamics in model photosynthetic systems

Huo

Coker

2012

Two-dimensional photon-echo experiments indicate that excitation energy transfer between chromophores near the reaction center of the photosynthetic purple bacterium Rhodobacter sphaeroides occurs coherently with decoherence times of hundreds of femtoseconds, comparable to the energy transfer time scale in these systems. The original explanation of this observation suggested that correlated fluctuations in chromophore excitation energies, driven by large scale protein motions could result in long lived coherent energy transfer dynamics. However, no significant site energy correlation has been found in recent molecular dynamics simulations of several model light harvesting systems. Instead, there is evidence of correlated fluctuations in site energy-electronic coupling and electronic coupling-electronic coupling. The roles of these different types of correlations in excitation energy transfer dynamics are not yet thoroughly understood, though the effects of site energy correlations have been well studied. In this paper, we introduce several general models that can realistically describe the effects of various types of correlated fluctuations in chromophore properties and systematically study the behavior of these models using general methods for treating dissipative quantum dynamics in complex multi-chromophore systems. The effects of correlation between site energy and inter-site electronic couplings are explored in a two state model of excitation energy transfer between the accessory bacteriochlorophyll and bacteriopheophytin in a reaction center system and we find that these types of correlated fluctuations can enhance or suppress coherence and transfer rate simultaneously. In contrast, models for correlated fluctuations in chromophore excitation energies show enhanced coherent dynamics but necessarily show decrease in excitation energy transfer rate accompanying such coherence enhancement. Finally, for a three state model of the Fenna-Matthews-Olsen light harvesting complex, we explore the influence of including correlations in inter-chromophore couplings between different chromophore dimers that share a common chromophore. We find that the relative sign of the different correlations can have profound influence on decoherence time and energy transfer rate and can provide sensitive control of relaxation in these complex quantum dynamical open systems.

“…32 An alternative approach of comparable numerical intensity is given by a path integral formulation. 33,34 We present an alternative and numerically less intensive approach which uses perturbation theory for part of the exciton-vibrational coupling. It will be shown how the nonMarkovian effects for a whole manifold of low-frequency protein vibrations can be included in the theory.…”

Section: Introductionmentioning

confidence: 99%

On the relation of protein dynamics and exciton relaxation in pigment–protein complexes: An estimation of the spectral density and a theory for the calculation of optical spectra

Renger¹,

Marcus²

2002

332

498

A theory for calculating time-and frequency-domain optical spectra of pigment-protein complexes is presented using a density matrix approach. Non-Markovian effects in the excitonvibrational coupling are included. A correlation function is deduced from the simulation of 1.6 K fluorescence line narrowing spectra of a monomer pigment-protein complex ͑B777͒, and then used to calculate fluorescence line narrowing spectra of a dimer complex ͑B820͒. A vibrational sideband of an excitonic transition is obtained, a distinct non-Markovian feature, and agrees well with experiment on B820 complexes. The theory and the above correlation function are used elsewhere to make predictions and compare with data on time-domain pump-probe spectra and frequencydomain linear absorption, circular dichroism and fluorescence spectra of Photosystem II reaction centers.