Representations of condensed-phase quantum dynamics and perturbative quantum master equations for energy transfer in molecular aggregates
Yuan-Chung Cheng, National Taiwan University
Developing accurate theories applicable for intermediate-coupling energy transfer dynamics in molecular systems has been a great research challenge. We have developed two perturbative approaches to undertake this challenge. The two methods are based on two distinct representations: a small polaronic basis that gives prominence to electron-phonon couplings versus a pure-dephasing basis that emphasizes electronic coherence. Second-order perturbative quantum master equations were derived in both representations and each benchmarked against numerically exact results of dynamics in a spin-boson model in a broad parameter space to examine their respective regimes of applicability. We showed that both methods yield accurate dynamics for a class of energy transfer problems in a wide parameter range, yet each still has its respective weakness due to the choice of the representations. Moreover, we demonstrated that simple accuracy criteria could be developed to assess the applicability regimes of the theories. Interestingly, a comparison demonstrates the complementary nature of the two representations, and as a result, the combination of the two methods provides accurate dynamics for the spin-boson model in the full parameter space investigated in this study. Finally, we will discuss several approaches that could be used to improve perturbative quantum master equations. These results should be useful for developing more accurate and efficient methods for simulations of energy transfer dynamics in molecular aggregate systems.
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