Collective Proton Tunneling in Ice?

氢键网络中的质子转移在许多化学、生物和工业过程中起着重要的作用。虽然单质子或双质子的质子转移过程中的量子效应已经得到了很好的模拟，但当涉及到集体运动引发的多体协同质子运动时，量子效应仍然难以捉摸。最近的实验提供了证据，表明涉及多达6个质子的协同隧道作用可能低于在普通六角形冰中在低温下观察到的非阿累尼乌斯质子动力学--然而，除了猜测之外，还缺乏任何机械解释。在这个项目中，将使用从头算路径积分模拟来研究所谓的六个质子在六角形冰中协同隧穿的机制。在这里，量子效应对于理解这一现象本质上是重要的，它不仅拓宽了分布函数，降低了自由能垒，通常被认为是小幅度零点振动的“微不足道”的结果。因此，可以预期，对集体质子隧穿的机械洞察将具有超越具体情况的广泛重要性。

Proton transfer in hydrogen-bonded networks plays an important role in many chemical, biological, and industrial processes. Although quantum effects on proton transfer involving a single proton or two protons are well investigated by simulation they remain elusive when it comes to many-body concerted proton motion triggered by collective motion. Recent experiments have provided evidence that concerted tunneling involving as many as six protons might underly the non-Arrhenius proton dynamics observed at low temperatures in ordinary hexagonal ice - yet any mechanistic explanations are lacking beyond speculations. In this project ab initio path integral simulations will be used to investigate the mechanism of the alleged concerted tunneling of six protons in hexagonal ice. Here, quantum effects are qualitatively important to understand the phenomenon, and do not only broaden distribution functions and lower free energy barriers as usually found as a "trivial" consequence of small-amplitude zero-point vibrations. It is thus expected that the mechanistic insights gained into collective proton tunneling will be of broad importance beyond the specific case.