Calculation of absorption spectra for light-harvesting systems using non-Markovian approaches as well as modified Redfield theory

Abstract

For an ensemble of B850 rings of the light-harvesting system LH2 of purple bacteria the linear absorption spectrum is calculated. Using different Markovian and non-Markovian, time-dependent and time-independent methods based on second-order perturbation theory in the coupling between the excitonic system and its surrounding environment as well as the modified Redfield theory, the influence of the shape of the spectral density on the linear absorption spectrum is demonstrated for single samples and in the ensemble average. For long bath correlation times non-Markovian effects clearly show up in the static absorption line shapes. Among the different spectral densities studied is one of the purple bacterium Rhodospirillum molischianum obtained by a molecular-dynamics simulation earlier. The effect of static disorder on its line shapes in the ensemble average is analyzed and the results of the present calculations are compared to experimental data.

Photosynthetic light harvesting: excitons and coherence

“…Redfield theory) can be considered to be a small perturbation. Moreover, the typical timescale associated with equilibration of the protein and solvent environment of chromophores in response to electronic excitation is often comparable with the timescale of excitation dynamics, adding a further challenging aspect for theory [57,62,63]. In addition, strong coupling to selective vibrations, for example of intramolecular origin, are commonplace in molecular systems [64][65][66].…”

Energy transfer in finite-size exciton-phonon systems: Confinement-enhanced quantum decoherence

“…Example among many are amide-I excitons in α-helices that favor the transduction of the chemical energy into mechanical work [2][3][4][5][6][7][8][9][10], vibrons in adsorbed nanostructures that enhance surface reactions or promote quantum information transfer [11][12][13][14][15], and Frenkel excitons in light-harvesting complexes that convert solar energy into chemical energy [16][17][18][19]. A molecular lattice exhibits regularly distributed atomic subunits along which the energy of an electronic transition, or of a high-frequency vibrational mode, delocalizes owing to dipole-dipole interaction.…”

Exact non-Markovian master equation for a driven damped two-level system

“…Now, we go to the details. Under a similar assumption, i.e., the factorized initial system-reservoir density matrix, the secondorder time-convolutionless master equation in the interaction picture can be obtained [2,[56][57][58][59][60][61][62][63] …”

“…(36) [2,[56][57][58][59][60][61][62][63]. One may wonder if the second order timenonlocal master equation (39) is more accurate than the second-order time-convolutionless master equation (41).…”