Carsten Olbrich, Thomas L. C. Jansen, Jörg Liebers, Mortaza Aghtar, Johan
Strümpfer, Klaus Schulten, Jasper Knoester, and Ulrich Kleinekathoefer.
From atomistic modeling to excitation transfer and two-dimensional
spectra of the FMO light-harvesting complex.
Journal of Physical Chemistry B, 115(26):8609-8621, 2011.
(PMC: 3140161)
OLBR2011A
The experimental observation of long-lived quantum coherences in the Fenna-Matthews-
Olson (FMO) light-harvesting complex at low temperatures has challenged general
intuition in the field of complex molecular systems and provoked considerable theoretical
effort in search for explanations. Here we report on room-temperature calculations of the
excited-state dynamics in FMO using a combination of molecular dynamics simulations
and electronic structure calculations. Thus we obtain trajectories for the Hamiltonian of
this system which contains time-dependent vertical excitation energies of the individual
bacteriochlorophyll molecules and their mutual electronic couplings. The distribution of
energies and couplings are analyzed together with possible spatial correlations. It is found
that in contrast to frequent assumptions the site energy distribution is non-Gaussian. In a
subsequent step, averaged wave packet dynamics is used to determine the exciton
dynamics in the system. Finally, with the time-dependent Hamiltonian linear and two-
dimensional spectra are determined. The thus obtained linear absorption lineshape agrees
well with experimental observation and is largely determined by the non-Gaussian site
energy distribution. The two-dimensional spectra are in line with what one would expect
by extrapolation of the experimental observations at lower temperatures and indicate
almost total loss of long-lived coherences.
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