Congratulations to our PhD student Piermarco Saraceno for his publication titled “Evaluation of approximate lineshape theories for photosynthetic light-harvesting antennae” in The Journal of Chemical Physics.This work examines the reliability of widely used approximate lineshape theories for modeling optical spectra in multichromophoric pigment–protein complexes, where excitonic and vibronic interactions are strongly intertwined.
By comparing cumulant‑based and Redfield‑type approaches against numerically exact HEOM calculations, the study reveals 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. Using chlorophyll dimers in WSCP and the multichromophoric antenna CP29, the authors show that non‑Markovian cumulant methods accurately capture vibronic intensities and exciton–vibration renormalization, while Markovian theories underestimate vibronic features and over‑broaden the main absorption band. Fluorescence spectra prove even more sensitive to these approximations, motivating the development of new equations for efficient non‑Markovian fluorescence calculations. These findings define the reliability range of approximate lineshape theories and provide guidance for accurate spectroscopic modeling of complex PPCs.
The paper is available at the following link: https://doi.org/10.1063/5.0310361
