title: Rate constants from instanton theory via a microcanonical approach.
abstract: Microcanonical instanton theory offers the promise of providing rate constants for chemical reactions including quantum tunneling of atoms over the whole temperature range. We discuss different rate expressions, which require the calculation of stability parameters of the instantons. The traditional way of obtaining these stability parameters is shown to be numerically unstable in practical applications. We provide three alternative algorithms to obtain such stability parameters for non-separable systems, i.e., systems in which the vibrational modes perpendicular to the instanton path couple to movement along the path. We show the applicability of our algorithms on two molecular systems: H2+ OH → H2O + H using a fitted potential energy surface and HNCO + H → NH2CO using a potential obtained on-the-fly from density functional calculations.
authors.affiliation: Institute for Theoretical Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany.
authors.forename: Sean R
authors.identifier: 0000000240864773
authors.initials: SR
authors.lastname: McConnell
authors.affiliation: Institute for Theoretical Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Löhle
authors.affiliation: Institute for Theoretical Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany.
authors.forename: Johannes
authors.identifier: 0000000161787669
authors.initials: J
authors.lastname: Kästner