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.