Faculty of Chemistry, University of Wrocław, 14 F. Joliot-Curie Str, 50-383 Wrocław, Poland.
J Mol Model. 2011 Nov;17(11):2995-3004. doi: 10.1007/s00894-011-1020-9. Epub 2011 Mar 1.
In the paper are described studies of the double proton transfer (DPT) processes in the cyclic dimer of acetic acid in the gas phase using Car-Parrinello (CPMD) and path integral molecular dynamics (PIMD). Structures, energies and proton trajectories have been determined. The results show the double proton transfer in 450 K. In the classical dynamics (CPMD) a clear process mechanism can be identified, where asynchronized DPT arises due to coupling between the O-H stretching oscillator and several low energy intermolecular vibrational modes. The DPT mechanism is also asynchronic when quantum tunneling has been allowed in the simulation. It has been found that the calculated values of barrier height for the proton transfer depends very strongly on the used approaches. Barrier received from the free-energy profile at the CPMD level is around 4.5 kcal mol(-1) whereas at the PIMD level is reduced to 1 kcal mol(-1). The nature of bonding in acetic acid dimer and rearrangement of electron density due to the proton movement has been also studied by the topological analysis of Electron Localization Function and Electron Localizability Indicator function.
本文使用 Car-Parrinello（CPMD）和路径积分分子动力学（PIMD）方法研究了气相中环己二乙酸的双质子转移（DPT）过程。确定了结构、能量和质子轨迹。结果表明在 450 K 下发生了双质子转移。在经典动力学（CPMD）中，可以清楚地识别出一个明确的反应机制，其中由于 O-H 伸缩振动振荡器与几个低能量的分子间振动模式的耦合，导致了非同步的 DPT。当允许模拟中量子隧穿时，DPT 机制也是异步的。研究发现，质子转移的势垒高度的计算值非常强烈地依赖于所使用的方法。在 CPMD 水平上得到的自由能曲线的势垒高度约为 4.5 kcal/mol，而在 PIMD 水平上则降低到 1 kcal/mol。通过电子定域函数和电子定域指标函数的拓扑分析，还研究了乙酸二聚体的成键性质和由于质子运动引起的电子密度重排。
