We summarized our developments of quasiparticle approaches for calculating 2D-IR spectra of e.g. liquid water, amylophybrils, and organic solute-solvent complexes. Two approaches molecular dynamics (MD-NEE) and phenomenologic stochastic models (SNEE) for modelling Hamiltonian fluctuations are revviewed.
In the present paper, we generalized previous contributions into the unified approach which includes both MD-NEE and SNEE (previously treated quite separately) as special cases.