Calculating nonlinear vibrational spectra from full quantum dynamics is generally impractical, while purely classical calculations may be qualitatively incorrect. The optimized mean-trajectory (OMT) approximation is a semiclassical method for computing nonlinear vibrational spectra from classical trajectories.   In the OMT approximation, dynamics of quantum coherences or populations are represented by action-quantized classical trajectories  linked by discrete jumps in action representing radiation-matter interactions.   An efficient numerical implementation allows the practical computation of two-dimensional spectra for multiple degrees of freedom. Through inclusion of numerical trajectories with the full anharmonic potential surface, the method incorporates effects of anharmonicity such as the generation of vibrational coherences forbidden under harmonic selection rules and the transfer of energy and coherence among resonantly coupled normal modes. Through a semiclassical treatment of electronic degrees of freedom, the OMT may be extended to vibronic spectra. The OMT provides a route to incorporating quantum effects in multidimensional optical spectra based on readily calculated classical trajectories.

Computing multidimensional optical spectra from classical trajectories

253rd National Meeting (2017)

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