Calculation of chemical reaction rate constants using on-the-fly high level electronic structure computations with...

The semiclassical instanton approach to the calculation of reaction rate constants at arbitrary temperatures in multiatomic systems is combined with high-level ab initio calculations of reactive potential energy surface (PES). The number of required ab initio calculations weakly depends on system size and allows on-the-fly evaluations of PES with high accuracy. The approach can be efficiently parallelized and provides a practical way of calculating quantum reaction rate constants with account of nuclear quantum effects such as multidimensional tunneling and zero point energies, which are rigorously incorporated in the theory. An algorithm for the search of instanton trajectories is explained. Application of the approach is illustrated for H + H(2) → H(2) + H and D + D(2) → D(2) + D bimolecular reactions in the wide temperature range with on-the-fly evaluation of PES at the ab initio full configuration interaction (FCI), coupled-cluster single double (CCSD), and single and double excitation configuration interaction (CISD) levels.