Real time quantum correlation functions. II. Maximum entropy numerical analytic continuation of path integral Monte Carlo and centroid molecular dynamics data

We propose a method which uses centroid molecular dynamics (CMD) [J. Cao an d G. A. Voth, J. Chem. Phys. 100, 5106 (1994)] real-time data in conjunctio n with the imaginary-time data generated using path integral Monte Carlo si mulations in a numerical analytic continuation scheme based on the maximum entropy approach. We show that significant improvement is achieved by inclu ding short-time CMD data with the imaginary-time data. In particular, for a particle bilinearly coupled to a harmonic bath, these methods lead to sign ificant improvements over previous calculations and even allow accurate det ermination of transport coefficients such as the diffusion coefficient and mobility for this system. In addition we show how maximum entropy method ca n be used to extract accurate dynamic information from short-time CMD data, and that this approach is superior to the direct Fourier transform of long -time data for systems characterized by broad, featureless spectral distrib utions. (C) 1999 American Institute of Physics. [S0021-9606(99)51744-3].