Linearized Path Integral Methods for Quantum Time Correlation Functions.

We review recently developed approximate methods for computing quantum time correlation functions based on linearizing the phase of their path integral expressions in the difference between paths representing the forward and backward propagators. Our focus here will be on problems that can be partitioned into two subsystems: One that is best described by a few discrete quantum states such as the high frequency vibrations or electronic states of molecules, and the other subsystem, "the bath", composed of the remaining degrees of freedom that will be described by a continuous representation. The general theory will first be developed and applied to model condensed phase problems. Approximations to the theory will be then made enabling applications to large scale realistic systems. [ABSTRACT FROM AUTHOR]