Real time quantum correlation functions. I. Centroid molecular dynamics ofanharmonic systems

We investigate the accuracy of the recently proposed centroid molecular dyn amics (CMD) method [J. Cao and G. A. Voth, J. Chem. Phys. 100, 5106 (1994)] in the presence of highly anharmonic steep short range repulsive potential s. Such potentials are often present in condensed phases and govern collisi ons between solvent particles. We compare the results of CMD simulations wi th exact quantum results for several model one- and two-dimensional nondiss ipative systems and a one-dimensional system under isobaric conditions. We show that, for nondissipative systems, CMD is accurate only for very short times, and is unable to reproduce the effects of quantum coherences, which play an important role in these few-dimensional systems. CMD gives much bet ter results under isobaric conditions. The correlation functions and the ge neral lineshape of the absorption cross-section in the dipole limit are wel l reproduced. This is primarily due to dephasing of quantum coherences thro ugh inhomogeneous broadening. (C) 1999 American Institute of Physics. [S002 1-9606(99)51644-9].