Quantum Mechanical Calculations of Time Correlation Functions for Neat Fluids

Abstract

A more direct calculation using the pair-product approximation to the propagator is also discussed. Using single-step approximations to the propagator, it is shown that real-time correlation functions can be expressed as integrals of smooth functions, and thus can be efficiently evaluated by Monte Carlo methods. Tests on a model anharmonic system coupled to a bath of 25 harmonie oscillators are presented, and in spite of the large number of degrees of freedom associated with such a setting, the method allows direct calculation of correlation functions at intermediate temperatures over short to intermediate time lengths. Initial work into applying the single step propagator methodology to a Lennard-Jones fluid is also discussed. The efforts to evaluate the multidimensional integral associated with the unique matrix elements present in such a high dimensional system are explained, along with preliminary results.