The modeling of the absorption lineshape for embedded molecules through a polarizable QM/MM approach

We present a computational strategy to simulate the absorption lineshape of a molecule embedded in a complex environment by using a polarizable QM/MM approach. This strategy is presented in two alternative formulations, one based on a molecular dynamics simulation of the structural fluctuations of the system and the other using normal modes and harmonic frequencies calculated on optimized geometries. The comparison for the case of a chromophore within a strongly inhomogeneous and structured environment, namely the intercalation pocket of DNA, shows that the MD-based approach is able to reproduce the experimental spectral bandshape. In contrast, the static approach overestimates the vibronic coupling, resulting in a much broader band.