Møller Kristian H, Otkjær Rasmus V, Hyttinen Noora, Kurtén Theo, Kjaergaard Henrik G
Department of Chemistry, University of Copenhagen , Universitetsparken 5, DK-2100 Copenhagen Ø, Denmark.
Department of Chemistry, University of Helsinki , POB 55, FIN-00014 Helsinki, Finland.
J Phys Chem A. 2016 Dec 29;120(51):10072-10087. doi: 10.1021/acs.jpca.6b09370. Epub 2016 Dec 19.
Based on a small test system, (R)-CH(OH)(OO·)CHCHO, we have developed a cost-effective approach to the practical implementation of multiconformer transition state theory for peroxy radical hydrogen shift reactions at atmospherically relevant temperatures. While conformer searching is crucial for accurate reaction rates, an energy cutoff can be used to significantly reduce the computational cost with little loss of accuracy. For the reaction barrier, high-level calculations are needed, but the highest level of electronic structure theory is not necessary for the relative energy between conformers. Improving the approach to both transition state theory and electronic structure theory decreases the calculated reaction rate significantly, so low-level calculations can be used to rule out slow reactions. Further computational time can be saved by approximating the tunneling coefficients for each transition state by only that of the lowest-energy transition state. Finally, we test and validate our approach using higher-level theoretical values for our test system and existing experimental results for additional peroxy radical hydrogen shift reactions in three slightly larger systems.
基于一个小型测试系统(R)-CH(OH)(OO·)CHCHO，我们开发了一种经济高效的方法，用于在与大气相关的温度下对过氧自由基氢转移反应实际应用多构象体过渡态理论。虽然构象体搜索对于准确的反应速率至关重要，但可以使用能量截止值来显著降低计算成本，而准确性损失很小。对于反应势垒，需要进行高水平计算，但对于构象体之间的相对能量，并不需要最高水平的电子结构理论。改进过渡态理论和电子结构理论的方法会显著降低计算出的反应速率，因此可以使用低水平计算来排除慢速反应。通过仅用最低能量过渡态的隧穿系数来近似每个过渡态的隧穿系数，可以进一步节省计算时间。最后，我们使用测试系统的更高水平理论值以及三个稍大系统中其他过氧自由基氢转移反应的现有实验结果来测试和验证我们的方法。
