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Title: Accuracy of second order perturbation theory in the polaron and variational polaron frames
Authors: Lee, C.K. 
Moix, J.
Cao, J.
Issue Date: 28-May-2012
Citation: Lee, C.K., Moix, J., Cao, J. (2012-05-28). Accuracy of second order perturbation theory in the polaron and variational polaron frames. Journal of Chemical Physics 136 (20) : -. ScholarBank@NUS Repository.
Abstract: In the study of open quantum systems, the polaron transformation has recently attracted a renewed interest as it offers the possibility to explore the strong system-bath coupling regime. Despite this interest, a clear and unambiguous analysis of the regimes of validity of the polaron transformation is still lacking. Here we provide such a benchmark, comparing second order perturbation theory results in the original untransformed frame, the polaron frame, and the variational extension with numerically exact path integral calculations of the equilibrium reduced density matrix. Equilibrium quantities allow a direct comparison of the three methods without invoking any further approximations as is usually required in deriving master equations. It is found that the second order results in the original frame are accurate for weak system-bath coupling; the results deteriorate when the bath cut-off frequency decreases. The full polaron results are accurate for the entire range of coupling for a fast bath but only in the strong coupling regime for a slow bath. The variational method is capable of interpolating between these two methods and is valid over a much broader range of parameters. © 2012 American Institute of Physics.
Source Title: Journal of Chemical Physics
ISSN: 00219606
DOI: 10.1063/1.4722336
Appears in Collections:Staff Publications

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