title: Locating Instantons in Many Degrees of Freedom.
abstract: We implemented and compared four algorithms to locate instantons, i.e., the most likely tunneling paths at a given temperature. These allow to calculate reaction rates, including atom tunneling, down to very low temperature. An instanton is a first-order saddle point of the Euclidean action in the space of closed Feynman paths. We compared the Newton-Raphson method to the partitioned rational function optimization (P-RFO) algorithm, the dimer method, and a newly proposed mode-following algorithm, where the unstable mode is directly estimated from the instanton path. We tested the algorithms on three chemical systems, each including a hydrogen transfer, at different temperatures. Overall, the Newton-Raphson turned out to be the most promising method, with our newly proposed mode following, being the fall-back option.
authors.affiliation: Computational Biochemistry Group, Institute of Theoretical Chemistry, University of Stuttgart , Stuttgart, Germany.
authors.forename: Judith B
authors.initials: JB
authors.lastname: Rommel
authors.affiliation: Gorlaeus Laboratories, LIC, Leiden University , Leiden, The Netherlands.
authors.forename: T P M
authors.initials: TP
authors.lastname: Goumans
authors.affiliation: Computational Biochemistry Group, Institute of Theoretical Chemistry, University of Stuttgart , Stuttgart, Germany.
authors.forename: Johannes
authors.initials: J
authors.lastname: Kästner