Stuttgart 2012 – wissenschaftliches Programm

Bereiche | Tage | Auswahl | Suche | Aktualisierungen | Downloads | Hilfe

MO: Fachverband Molekülphysik

MO 18: Molecular Dynamics

MO 18.2: Vortrag

Donnerstag, 15. März 2012, 14:30–14:45, V38.02

Improvements to the Instanton Method: Tunneling in Large Systems — •Judith B. Rommel and Johannes Kästner — Institute of Theoretical Chemistry, University of Stuttgart, Germany

Quantum tunneling of atoms has a major impact on chemical reactions, in particular on reactions including hydrogen transfers. The enzyme glutamate mutase catalyzes a radical reaction involving two hydrogen transfers. We found the hydrogen transfers to be rate limiting [1]. The experimentally found kinetic isotope effects ranging from 6 to 30 suggest hydrogen tunneling. An improved path-integral-based instanton approach is used to figure out how the enzyme modulates these effects. The calculation of tunneling rates and kinetic isotope effects in systems with several hundred degrees of freedom like enzymes requires to locate the instanton via an optimization. We found a quadratically converging Newton-Raphson method to be better than mode following methods. The tangent mode method, recently proposed by us, turned out to be the fall-back option [2]. A variable step size formulation of the instanton rate theory allows to distribute sampling points more evenly along the bounce. Therefore, less sampling points are necessary which significantly reduces the computational effort [3].

[1] J.B. Rommel, J. Kästner, J. Am. Chem. Soc., 133, 10195, 2011.

[2] J.B. Rommel, T.P.M. Goumans, J. Kästner,

J. Chem. Theory Comput., 7, 690, 2011.

[3] J.B. Rommel, J. Kästner, J. Chem. Phys., 134, 84107, 2011.