ABSTRACT
In this chapter, we use the recently developed partial linearized den-
sity matrix (PLDM) propagation approach to explore the excitation
energy transfer dynamics in various light-harvesting systems. We
demonstrate that PLDM propagation can capture both short-time
nonequilibrium coherent dynamics, and recover long-time thermal
populations that result from relaxation of initial excitation in the
model dissipative environment of protein-pigment photosynthetic
light-harvesting complexes. We find that the energy transfer rate
can be optimized as a function of the strength of the system-
environment interactions. Despite the fact that experiments show
signatures of coherent dynamics at short times we find that such
features play little role in controlling the energy transfer rate. We
show that the presence of coherent beating in chromophore net-
work populations, which matches closely with features observed in
nonlinear 2D spectroscopy signals, is strongly dependent on theway
the excitation is injected into the multichromophore network. The
artificial initial conditions employed in the experiments enhance
the coherence and with more realistic initialization the coherent
features are significantly diminished. We show that a simple
kinetic model can be used to understand the population dynamics
and relaxation to thermal equilibrium in these systems. Our
calculations employing various realistically parameterized model
Hamiltonians for photosynthetic light-harvesting systems explore
the effects initialization, the influence of strongly coupled dimers
that result in quantum coherent beating, and the effect of correlated
bath fluctuations in diagonal and off-diagonal elements of the
system-bath Hamiltonian over realistic parameter ranges for these
systems.
