On-the-fly ab initio calculations toward accurate rate coefficients

Abstract

During automatic kinetic model generation a large number of reactions need to have kinetic data assigned to them. One of the main challenges is on how to account for the large scarcity of accurate data. The ever-growing computational power and availability of high performance computing solutions allows to envisage implementing on-the-fly ab initio calculations for a large number of reaction rate coefficients. Today extensive user knowledge and involvement is required to develop fast and effective ab initio based kinetic models. The present work introduces a series of automation procedures to minimize user involvement. It allows automated quantum chemical calculations for a large number of reactions for gas-phase processes with a wide variety in chemical species. 3D coordinates are calculated for all the reactants, products and transition states and automatically submitted to quantum chemistry packages. The latter yield accurate high-pressure limit rate coefficients. All steps are automated without the need for manual interventions, even for recognizing rotational frequencies and for verifying whether the saddle point searches lead to the appropriate transition state. A good agreement to literature data is found, i.e., most of the rate coefficients are within a factor of 2 of literature data.