The importance of the pre-exponential factor in semiclassical molecular dynamics

This paper deals with the critical issue of approximating the pre-exponential factor in semiclas-
sical molecular dynamics. The pre-exponential factor is important because it accounts for the
quantum contribution to the semiclassical propagator of the classical Feynman path fluctuations.
Pre-exponential factor approximations are necessary when chaotic or complex systems are simulated.
We introduced pre-exponential factor approximations based either on analytical considerations or
numerical regularization. The approximations are tested for power spectrum calculations of more and
more chaotic model systems and on several molecules, for which exact quantum mechanical values
are available. The results show that the pre-exponential factor approximations introduced are accurate
enough to be safely employed for semiclassical simulations of complex systems.