| Although the development of modern physics has been able to understand and describe many basic physics progresses, there are still problems that cannot be quantitatively interpreted or predicted using present theory. For example, we cannot directly deduce the evolution of life using basic theory, or accurately predict the lifetime of the single crystal materials. Similarly, we still do not know how to predict the stability of nano-devices or the thermal-driven chemical reaction rates. The latter question is closely related with the design of new molecules and materials, and even the pharmacokinetics and the evolvement of atmosphere, oceans or soil. The essence of these problems is how to theoretically predict the thermal-driven atomic migration rates. Transition state theory is the most commonly used rate theory, which has been developed for about eighty years. In this theory a system is described as thermodynamic quasi-equilibrium and the thermal-driven atomic migration rate is given via statistical physics methods. Although this theory presents a clear physical picture, the predicted rate constants are often different with the experimental observations in orders of magnitude because of the different artificial chosen parameters. Generally, a reasonable explanation for the observed experimental data can be given by the transition state theory with specific parameters, but the prediction ability of the transition state theory is seriously challenged in designations of desired chemical reactions. Therefore, it is very necessary to build an uniform physics model without empirical parameters for predicting the thermal reaction rate.The recently established physics model based on the statistics of individual atom (EPL94,40002(2011)) has been successfully applied to predict the lifetime of the nano-devices and the adatom diffusion rates on solid surfaces. In the present work this model was promoted to predict the thermal-driven chemical reaction rates without experimental parameters, and it successfully predicted the rate constants of elementary unimolecular and bimolecular reactions. Some experimental results of unimolecular dissociation reactions such as CH4â†'CH3+H, CH3OHâ†'CH3+OH and CF3CH2Clâ†'CF2CHCI+HF, as well as bimolecular collision reactions S+SO2â†'SO+SO and NH3+Clâ†'H2+HC1, were chosen to compare with our model and the transition state theory. The rate constants of these reactions have measured in a wide temperature range. To perform the transition state theory, some complex parameters such as the partition functions of different chemical structures are needed, while our model need only two to three theoretical parameters, like static potential barriers, the reaction variation or the effective cross-sections. And such the parameters in our theoretical framework are very easy to be obtained without empirical parameters. The results show that the individual-atomic statistical model is more precise than the transition state theory. Considering molecular dynamics simulations can give the detail of motions for each atom in a system without taking any quantum effects into account, it provides more accurate and reliable rate data than the experiments and suitable to strictly verify the validation of our model. In this work, we performed molecular dynamics simulations for the isomerization of C60and the collision reaction of C60+C60â†'C120, and the results are in good agreement with individual-atomic statistical model, while far away from the conventional transition state theory, which gives differences with the molecular dynamics simulations in several orders of magnitude in higher temperature range. |
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