Calculating approximate quantum mechanical rates without an a priori reaction coordinate

摘要

Two distinct reaction path methods are combined with the imaginary time centroid formalism to yield an approximate means of computing effective quantum rates without a preconceived notion of a reaction coordinate or transition state. The first method, which combines the imaginary time centroid formalism with the determination of minimum energy pathways, is appropriate for use when energetic factors dominate the rate process. The second utilizes an approximate determination of an effective centroid potential and the transition path sampling method of Chandler and co-workers, an approach designed for reactions that occur on more complex landscapes. The two methods are applied to the isomerization of a seven-atom argon cluster at 5K where quantum effects are relevant.