Department of Applied Biology and Chemical Technology, Hong Kong Polytechnic University, Hung Hom, Hong Kong.
J Comput Chem. 2013 Mar 15;34(7):545-57. doi: 10.1002/jcc.23163. Epub 2012 Nov 1.
The minimum energy path (MEP) of the reaction, CF(3)CHFCF(3) + H → transition state (TS) → CF(3)CFCF(3) + H(2), has been computed at different ab initio levels and with density functional theory (DFT) using different functionals. The computed B3LYP/6-31++G**, BH&HLYP/cc-pVDZ, BMK/6-31++G**, M05/6-31+G**, M05-2X/6-31+G**, UMP2/6-31++G**, PUMP2/6-31++G**//UMP2/6-31++G**, RCCSD(T)/aug-cc-pVDZ//UMP2/6-31++G**, RCCSD(T)/aug-cc-pVTZ(spd,sp)//UMP2//6-31++G**, RCCSD(T)/CBS//M05/6-31+G**, and RCCSD(T)/CBS//UMP2/6-31++G** MEPs, and associated gradients and Hessians, were used in reaction rate coefficient calculations based on the transition state theory (TST). Reaction rate coefficients were computed between 300 and 1500 K at various levels of TST, which include conventional TST, canonical variational TST (CVT) and improved CVT (ICVT), and with different tunneling corrections, namely, Wigner, zero-curvature, and small-curvature (SCT). The computed rate coefficients obtained at different ab initio, DFT and TST levels are compared with experimental values available in the 1000-1200 K temperature range. Based on the rate coefficients computed at the ICVT/SCT level, the highest TST level used in this study, the BH&HLYP functional performs best among all the functionals used, while the RCCSD(T)/CBS//MP2/6-31++G** level is the best among all the ab initio levels used. Comparing computed reaction rate coefficients obtained at different levels of theory shows that, the computed barrier height has the strongest effect on the computed reaction rate coefficients as expected. Variational effects on the computed rate coefficients are found to be negligibly small. Although tunneling effects are relatively small at high temperatures (1500 K), SCT corrections are significant at low temperatures (300 K), and both barrier heights and the magnitudes of the imaginary frequencies affect SCT corrections.
反应的最小能量路径（MEP），CF(3)CHFCF(3) + H → 过渡态（TS）→ CF(3)CFCF(3) + H(2)，已经在不同的从头算水平和密度泛函理论（DFT）下使用不同的泛函进行了计算。所计算的 B3LYP/6-31++G**、BH&HLYP/cc-pVDZ、BMK/6-31++G**、M05/6-31+G**、M05-2X/6-31+G**、UMP2/6-31++G**、PUMP2/6-31++G**//UMP2/6-31++G**、RCCSD(T)/aug-cc-pVDZ//UMP2/6-31++G**、RCCSD(T)/aug-cc-pVTZ(spd,sp)//UMP2//6-31++G**、RCCSD(T)/CBS//M05/6-31+G和 RCCSD(T)/CBS//UMP2/6-31++G MEP，以及相关的梯度和 Hessian，用于基于过渡态理论（TST）的反应速率系数计算。在不同的 TST 水平下，在 300 到 1500 K 的温度范围内计算了反应速率系数，其中包括常规 TST、正则变分 TST（CVT）和改进 CVT（ICVT），以及不同的隧道校正，即 Wigner、零曲率和小曲率（SCT）。在不同的从头算、DFT 和 TST 水平上计算的反应速率系数与 1000-1200 K 温度范围内可用的实验值进行了比较。基于在 ICVT/SCT 水平上计算的速率系数，这是本研究中使用的最高 TST 水平，BH&HLYP 泛函在所有使用的泛函中表现最好，而 RCCSD(T)/CBS//MP2/6-31++G** 水平在所有使用的从头算水平中表现最好。比较在不同理论水平上计算得到的反应速率系数表明，计算得到的势垒高度对计算得到的反应速率系数的影响最强，这是预期的。在计算得到的速率系数中发现变分效应可以忽略不计。尽管在高温（1500 K）下隧道效应相对较小，但 SCT 校正在低温（300 K）下非常显著，并且势垒高度和虚频的幅度都影响 SCT 校正。
