The generalized time dependent perturbation theory developed for the real time SCIVR methodology can also be used within a thermodynamic context. One can develop Gaussian approximations to the thermal (imaginary time) propagator and then employ the generalized time dependent perturbation theory to obtain the numerically exact thermodynamics [9,10]. This methodology is also amenable to on the fly computations and so can in principle become rather powerful. It can also be used within the real time context, for the computation of thermal correlation functions without the necessity of assuming factorized initial conditions. Initial applications of this methodology include the thermodynamics of rare gas clusters at very low temperatures .