title: Microcanonical and thermal instanton rate theory for chemical reactions at all temperatures.
abstract: Semiclassical instanton theory is used to study the quantum effects of tunnelling and delocalization in molecular systems. An analysis of the approximations involved in the method is presented based on a recent first-principles derivation of instanton rate theory [J. Chem. Phys., 2016, 144, 114106]. It is known that the standard instanton method is unable to accurately compute thermal rates near the crossover temperature. The causes of this problem are identified and an improved method is proposed, whereby an instanton approximation to the microcanonical rate is defined and integrated numerically to obtain a thermal rate at any temperature. No new computational algorithms are required, but only data analysis of a number of standard instanton calculations.
authors.affiliation: Department of Chemistry, Durham University, South Road, Durham, DH1 3LE, UK and Laboratory of Physical Chemistry, ETH Zurich, 8093 Zurich, Switzerland. jeremy.richardson@phys.chem.ethz.ch.
authors.forename: Jeremy O
authors.identifier: 0000-0002-9429-151X
authors.initials: JO
authors.lastname: Richardson