Partition functions for reaction rate calculations:: statistical sampling and MCTDH propagation

An approach for the accurate calculation of partition functions is introduced. It employs the multi-configurational time-dependent Hartree (MCTDH) approach to propagate wave packets in imaginary time. The initial wave packets to be propagated are obtained from a statistical sampling scheme. The scheme facilitates the efficient calculation of reactant partition functions required in accurate reaction rate calculations. As an example, the vibrational partition function of methane is studied. (C) 2001 Elsevier Science B.V. All rights reserved.