Modeling optical spectra of multichromophoric systems requires capturing the interplay between excitonic and vibronic dynamics. In our latest study, we benchmark several approximate lineshape theories against numerically exact calculations, using chlorophyll dimers in WSCP and the light-harvesting complex CP29.
We show that the well‑known suppression of vibronic sidebands originates primarily from the Markov approximation applied to off‑diagonal system–bath couplings, rather than from the perturbative order of the theory. Non‑Markovian cumulant approaches instead reproduce vibronic intensities and exciton–vibration renormalization. Fluorescence spectra are even more sensitive to these approximations, motivating the development of new equations for efficient non‑Markovian fluorescence calculations. Overall, this work defines the reliability range of approximate lineshape theories and clarifies when more accurate treatments are required for interpreting PPC spectra.
P. Saraceno, A. Bhartiya, J. Seibt, T. Renger, T. Kramer, L. Cupellini,
Evaluation of approximate lineshape theories for photosynthetic light-harvesting antennae
J. Chem. Phys. 2026, 164, 044119, DOI: 10.1063/5.0310361