Simple and efficient theoretical approach to compute 2d optical spectra

A highly efficient scheme is proposed and benchmarked to compute 2D optical spectra. This scheme is ideally designed for electronic spectroscopy; however, the method can be applied in a straightforward way to vibrational spectroscopy as well. Our scheme performs dynamics only for the t ₂ duration, eliminating explicit t ₁ and t ₃ coherent dynamics and thus can achieve dramatic improvements in efficiency. To gain this efficiency, we assume the system is in the inhomogeneous regime and that there is no significant nonadiabatic transfer of population during the t ₁ and t ₃ coherence times. Preliminary results are presented for the Frenkel Hamiltonian. We obtain excellent agreement with numerically exact results (which are possible for this simplistic model Hamiltonian), capturing all relevant trends at least qualitatively (and sometimes quantitatively).