Quantum Instanton Evaluations of the Thermal Rate Constants for Complex Systems

Quantum instanton (QI) approximation is recently proposed for the evaluations of the chemical reaction rate constants with use of full dimensional potential energy surfaces. Its strategy is to use the instanton mechanism and to approximate time-dependent quantum dynamics to the imaginary time propagation of the quantities of partition function. It thus incorporates the properties of the instanton idea and the quantum effect of partition function and can be applied to chemical reactions of complex systems. In this paper, we present the QI approach and its applications to several complex systems mainly done by us. The concrete systems include, (1) the reaction of H+CH4→H2+CH3, (2) the reaction of H+SiH4→H2+SiH3, (3) H diffusion on Ni(100) surface; and (4) surface-subsurface transport and interior migration for H/Ni. Available experimental and other theoretical data are also presented for the purpose of comparison.

THE RATE CONSTANT OF THE O(3P) + HCl → OH + Cl REACTION WITHIN QUANTUM INSTANTON APPROXIMATION

Temperature dependence of the rate constant of the O (3 P ) + HCl → OH + Cl reaction was calculated for 200–700 K range within the quantum instanton approximation using the 3A″ potential energy surface. Curvature of the Arrhenius plot arising from quantum effects in the hydrogen exchange reaction was observed. Results of the present method were found to significantly improve upon those obtained within the ICVT/μOMT method. The errors pertaining to the present method were estimated.