Abstract
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.
Highlights
The accurate and efficient evaluation of chemical reaction rate constant is one of prime objectives of theoretical reaction dynamics
Comparing the quantum instanton rates with others, we find that kQI is in good agreement with the experimental data it is closer to the rates obtained by Baulch et al [47] than those by Sutherland et al [48], and kQI agrees with kCVT/μOMT within 10% for the temperature range T = 600–2000 K, but it becomes somewhat larger than the latter as the temperature is decreased
We explore the evaluation of the quantum instanton approximation to the process of H diffusion on Ni(100) surface using the EAM4 potential energy surface constructed by Truong and Truhlar [53]
Summary
The accurate and efficient evaluation of chemical reaction rate constant is one of prime objectives of theoretical reaction dynamics. Benefited from the small recrossing dynamics at not-toohigh temperatures, the transition state theories (TSTs), originally proposed by Eyring [1, 2] and Wigner [3], have become a possible and popular way to estimate rate constants. Due to their practical simplicity, they have been broadly applied to numerous reactions. Since the QI solely involves the Boltzmann operator and its relevant quantities, it can be applied to quite complex molecular systems (from gas phase [17, 37], liquid [28], to surface [38, 39]) via well-established imaginary time path integral techniques. The systems include two gas phase reactions H + CH4 → H2 + CH3 [17] and H + SiH4 → H2 + SiH3 [37], H diffusion on Ni(100) surface [38], and surface-subsurface transport and interior migration for H/Ni [39]
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