Critical tests of a new master equation approach to nonadiabatic quantum dissipative systems

Using the spin-boson model as an example, we test the accuracy of a new master equation approach to quantum dissipative problems. The master equation approach is based an approximate resummation to all orders in the nonadiabatic coupling of the exact memory kernel as well as an inhomogeneous term that represents the effects of nonequilibrium preparation. The method is tested against recent numerically exact calculations of Thoss et al. in the difficult region of parameter space for which several energy scales are comparable. The asymptotic behavior of population correlations at zero temperature are also investigated. The method proves to be remarkably accurate in such cases. Finally, we discuss the extension of the method for anharmonic baths, nonlinear coupling and multiple electronic states