Abstract
We present a partially linearized method based on spin-mapping for computing both linear and nonlinear optical spectra. As observables are obtained from ensembles of classical trajectories, the approach can be applied to the large condensed-phase systems that undergo photosynthetic light-harvesting processes. In particular, the recently derived spin partially linearized density matrix method has been shown to exhibit superior accuracy in computing population dynamics compared to other related classical-trajectory methods. Such a method should also be ideally suited to describing the quantum coherences generated by interaction with light. We demonstrate that this is, indeed, the case by calculating the nonlinear optical response functions relevant for the pump-probe and 2D photon-echo spectra for a Frenkel biexciton model and the Fenna-Matthews-Olsen light-harvesting complex. One especially desirable feature of our approach is that the full spectrum can be decomposed into its constituent components associated with the various Liouville-space pathways, offering a greater insight beyond what can be directly obtained from experiments.
Highlights
Nonlinear optical spectroscopy is a powerful tool for elucidating the exciton dynamics of condensed-phase systems.[1]
After first reviewing how linear optical spectra can be calculated with fully linearized semiclassical (LSC) mapping methods, we introduce our approach for calculating both linear and nonlinear spectra with spin-partially linearized density matrix (PLDM)
We have shown how classical-trajectory mappingbased methods can be used to compute optical spectra for nonadiabatic systems through the constituent response functions
Summary
Nonlinear optical spectroscopy is a powerful tool for elucidating the exciton dynamics of condensed-phase systems.[1]. Progress has been made in improving the accuracy of such methods through the use of a resolution of the identity,[28,29] optimized zero-point energy parameters,[30,31] the generalized master equation,[32] nonadiabatic ring-polymer molecular dynamics,[33] symmetric windowing (SQC),[34] spin-mapping,[35,36] and other alternative classical mapping models.[37–40] Some of these advancements have already been used to obtain both linear and nonlinear optical spectra.[11,41–44] A successful method for computing dynamical observables within exciton systems is the standard partially linearized density matrix (PLDM)[45–48] approach, which uses coherent states within the MMST mapping space to describe the dynamics associated with the forward and backward exciton paths separately through the use of two independent sets of mapping variables. To the authors’ knowledge, no mappingbased approach has previously tackled the nonlinear spectra of such a large system
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