Practical evaluation of condensed phase quantum correlation functions:a feynman-kleinert variational linearized path integral method

摘要

We report a new method for calculating the Wigner transform of the Boltzmann operator in the canonial ensemble.The transform is accomplished by writing the Boltzmann operator in a semiharmonic form,utilizaing the variational centroid effective frequencies introduced by feynaman and Kleinerg (FK).The approsimate many-body Wigner transformed Boltzmann operator is then utilized with a linearized path integral (LPI)representation for correlation functions.it is shown that this new FK-LPI method is capable of calculating quite accurately the short time behavior of linear and highly nonlinear correlation functions for low temperature lennard-Jones model systems and that it is vastly superior to classical dynamics.The feasibility of the FK-LPI mthod for large systems is illustrated by considering a model liquid composed of 32 oxygen molecules with periodic boundary conditions.Initial conditions for molecular synamics are obtained from its Boltzmann Weigner transform and the FK-LPI method is shown to describe correctly the zero-point motion of the liquid.the effective frequency representation of the Wigner transformed thermal density operation provides and efficient way of sampling nonclassical initial conditions for molecular-dynamics simulations in complex molecular systems are discussed.