Isotope Effects in Water: Differences of Structure, Dynamics, Spectrum, and Proton Transport between Heavy and Light Water from ReaxFF Reactive Force Field Simulations

Investigating properties of both heavy and light water at the atomistic level is essential to understanding chemical and biological processes in aqueous solution. However, appropriately describing their difference on the nanoscale is still challenging. Employing ReaxFF reactive molecular dynamics simulations, we systematically study the structure, dynamics, and spectra of heavy and light water. With the water force field potential we developed, the different features between heavy and light water can be simulated appropriately by the classical treatment on large size and time scale. Here, we also report the structural difference between D3O+ and H3O+ in bulk heavy/light water. In addition, the diffusion constants of heavy and light water are successfully reproduced, and the Grotthuss hopping mechanism of proton transport in liquid water is properly described as well. It allows us to study a complex system in heavy/light aqueous environments, such as proton transport, chemical reaction, and tracing the reaction mechanism with an isotope substitute.在原子尺度下探究重水（heavy water）与轻水（light water）的理化性质，对于理解水溶液中的化学与生物过程至关重要。然而，在纳米尺度下精准刻画二者的差异仍颇具挑战。本研究采用ReaxFF反应分子动力学模拟方法，系统探究了重水与轻水的结构、动力学特性与光谱特征。借助我们开发的水势能力场，可通过大体系、长时程的经典力学处理，准确复现重水与轻水之间的差异特征。本研究还报道了本体重水与本体轻水中，氘合氢离子（D3O+）与水合氢离子（H3O+）的结构差异。此外，本研究成功复现了重水与轻水的扩散系数，并准确刻画了液态水中质子传递的格罗特斯跳跃（Grotthuss hopping）机制。该工作为我们在重水/轻水水溶液环境中开展复杂体系研究提供了可能，例如利用同位素替代开展质子传递、化学反应及反应机理追踪等相关研究。