Simulations of absorption and fluorescence lineshapes using the reaction coordinate method

Absorption and fluorescence lineshapes reflect a complex interplay between electronic and vibrational dynamics in molecular aggregates. Entanglement between the electronic system and vibrational bath poses a considerable challenge to accurate spectroscopic simulations. It can be described by accounting for at least some of the bath explicitly. Recently such type of approach formulated in terms of a reaction coordinate master equation was proposed (Iles-Smith et al., 2014). It is based on the reaction coordinate mapping, which permits to identify the most influential collective bath modes and include them into an enlarged system explicitly. Here we extend this reaction coordinate method (RCM) for calculations of absorption and fluorescence lineshapes. We apply the theory to a model dimer and obtain excellent agreement with exact results calculated with hierarchical equations of motion. This suggests that the RCM approach is applicable for simulations of linear and non-linear spectra of molecular aggregates.