Using Efficient Predictor-Corrector Reaction Path Integrators for Studies Involving Projected Frequencies.

Projected frequencies along a reaction pathway are necessary for computing reaction rates using variational transition state theory or reaction path Hamiltonian methods. The projected frequency analysis is quite sensitive to the accuracy of the reaction path integration. This work demonstrates that second- and first-order predictor-corrector reaction path integrators can be used for computing projected frequencies with high confidence. It is shown that these methods perform equally well with a variety of numerical integration step sizes and that, without a substantive loss in accuracy, Hessian updating can be used with both methods for stepping along the reaction path at points between those where projected frequencies are required.