  The recently introduced multisite tensor network path integral (MS-TNPI)
allows simulation of extended quantum systems coupled to dissipative media. We
use MS-TNPI to simulate the exciton transport and the absorption spectrum of a
B850 bacteriochlorophyll (BChl) ring. The MS-TNPI network is extended to
account for the ring topology of the B850 system. Accurate molecular
dynamics-based description of the molecular vibrations and the protein scaffold
is incorporated through the framework of Feynman-Vernon influence functional.
To relate the present work with the excitonic picture, an exploration of the
absorption spectrum is done by simulating it using approximate and
topologically consistent transition dipole moment vectors. Comparison of these
numerically exact MS-TNPI absorption spectra are shown with second-order
cumulant approximations. The effect of temperature on both the exact and the
approximate spectra is also explored.
