On the accuracy of the Pade-resummed master equation approach to dissipative quantum dynamics

Well--defined criteria are proposed for assessing the accuracy of quantum master equations whose memory functions are approximated by Pad\'e resummation of the first two moments in the electronic coupling. These criteria partition the parameter space into distinct levels of expected accuracy, ranging from quantitatively accurate regimes to regions of parameter space where the approach is not expected to be applicable. Extensive comparison of Pad\'e--resummed master equations with numerically exact results in the context of the spin--boson model demonstrate that the proposed criteria correctly demarcate the regions of parameter space where the Pad\'e approximation is reliable. The applicability analysis we present is not confined to the specifics of the Hamiltonian under consideration and should provide guidelines for other classes of resummation techniques.