  Photo-active systems are characterized by their capacity of absorbing light
energy and transforming it. Usually, more than one chromophore is involved in
the light absorption and excitation transport processes in complex systems.
Linear-Response Time-Dependent Density Functional (LR-TDDFT) is commonly used
to identify excitation energies and transition properties by solving well-known
Casida's equation for single molecules. However, this methodology is not useful
in practice when dealing with multichromophore systems. In this work, we extend
our local density decomposition method that enables to disentangle individual
contributions into the absorption spectrum to computation of exciton dynamic
properties, such as exciton coupling parameters. We derive an analytical
expression for the transition density from Real-Time Propagation TDDFT
(P-TDDFT) based on Linear Response theorems. We demonstrate the validity of our
method to determine transition dipole moments, transition densities and exciton
coupling for systems of increasing complexity. We start from the isolated
benzaldehyde molecule, perform a distance analysis for $\pi$-stacked dimers and
finally map the exciton coupling for a 14 benzaldehyde cluster.
