Multi Dimensional Quantum Dynamics of Chemical Reaction Processes

Abstract

Accurate quantum determination of the ground state tunneling splitting zero-point energy using the full dimensional potential proposed by Yagi et al. [J. Chem. Phys. 115:10647, 2001] are reported. Two exact quantum dynamics methods are used: the multi-configurational time-dependent Hartree (MCTDH) approach and the diffusion Monte Carlo based projection operator imaginary time spectral evolution (POITSE) method. In this report, we focus on the challenges faced by the MCTDH approach and the steps taken for obtaining the benchmark value. The MCTDH computation yields 25 cm−1 converged to about 10% accuracy while POITSE obtains a value for the tunneling splitting of 25.7±0.3 cm−1 which compares well with the experimental value of 21.6 cm−1. These rigorous results are used to evaluate the accuracy of approximate dynamical approaches, e.g. the instanton theory.