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作用。虽然单质子或双质子质子转移的量子效应已经通过模拟得到了很好的研究，但当涉及到由集体运动引发的多体协同质子运动时，量子效应仍然是难以捉摸的。最近的实验提供了证据，表明在低温下在普通六边形冰中观察到的非阿克里乌斯质子动力学可能是由多达6个质子参与的协同隧穿引起的，但除了猜测之外，还缺乏任何机械解释。在这个项目中，从头算路径积分模拟将被用来研究六个质子在六边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在性质上是重要的，并且不仅拓宽了分布函数和降低了自由能垒，这通常被认为是小振幅零点振动的“微不足道”的结果。因此，预计集体质子隧穿机制的见解将具有广泛的重要性超出了具体的情况。

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.