title: Quantum Tunneling Rates of Gas-Phase Reactions from On-the-Fly Instanton Calculations.
abstract: The instanton method obtains approximate tunneling rates from the minimum-action path (known as the instanton) linking reactants to the products at a given temperature. An efficient way to find the instanton is to search for saddle-points on the ring-polymer potential surface, which is obtained by expressing the quantum Boltzmann operator as a discrete path-integral. Here we report a practical implementation of this ring-polymer form of instanton theory into the Molpro electronic-structure package, which allows the rates to be computed on-the-fly, without the need for a fitted analytic potential-energy surface. As a test case, we compute tunneling rates for the benchmark H + CH4reaction, showing how the efficiency of the instanton method allows the user systematically to converge the tunneling rate with respect to the level of electronic-structure theory.
authors: Department of Chemistry, University of Cambridge , Lensfield Road, Cambridge, CB2 1EW, United Kingdom.
authors: Adrian N
authors: AN
authors: Beyer
authors: Department of Chemistry, University of Cambridge , Lensfield Road, Cambridge, CB2 1EW, United Kingdom.|Department of Chemistry, Durham University , South Road, Durham, DH1 3LE, United Kingdom.
authors: Jeremy O
authors: JO
authors: Richardson
authors: School of Chemistry, Cardiff University , Main Building, Park Place, Cardiff, CF10 3AT, United Kingdom.
authors: Peter J
authors: PJ
authors: Knowles
authors: Department of Chemistry, University of Cambridge , Lensfield Road, Cambridge, CB2 1EW, United Kingdom.
authors: Judith
authors: J
authors: Rommel
authors: Department of Chemistry, University of Cambridge , Lensfield Road, Cambridge, CB2 1EW, United Kingdom.
authors: Stuart C
authors: SC
authors: Althorpe