Water structure and dynamics at the solid/liquid interface from ab initio simulations

该项目旨在对固体/水界面的水结构和弛豫动力学进行微观理解。我们的目标是提供一个分子的理解如何的顺序和动态的界面水的pH值的函数，即表面质子化和电荷状态的变化。作为进一步的步骤，我们还旨在了解不同的离子在水固体界面的作用。我们将专注于选定的系统，即CaF 2/水界面，将进行并行模拟和实验分析。特别是，我们将进行基于密度泛函理论的从头计算模拟，而E。位于美因茨的马克斯普朗克聚合物研究所的巴克斯将进行SFG振动测量。这里的一个创新方面是使用从头计算模拟在分子水平上直接解释实验。第一原理模拟特别适合于建模接口，因为它们自然包括在异质环境中发生的极化效应（包括电子极化）。此外，它们还自然地包括温度效应和熵效应的采样。由于最近在代码优化和超级计算资源的可用性方面取得的进展，模拟所需的时间大大减少。因此，在实验和模拟中的数据采集需要类似的时间。我们想要解决的问题包括：（I）溶剂有序化，特别强调它延伸多远以及它如何受到表面质子化状态和表面电荷密度的影响。什么是溶剂在界面处的振动特性，以及它们如何从速度-速度（和表面特定）相关函数推导出来？(II)界面处的静电势。电势如何取决于pH值，与实验相比如何？(III)从局域振动激发的简正模开始描述界面处的能量弛豫。(IV)界面离子的影响。特别是，我们想解决如何不同的离子（简单的卤化物与分子离子）定位在界面上。直接靠近表面水分子的阴离子或扩散离子云中的阴离子如何影响水的有序性并改变界面处水的振动性质？特别是两个原型的情况下，将被视为，即Cl-和SO 42-。在这种情况下，我们也将研究动力学和能量弛豫。这里的关键问题是溶剂能量弛豫如何受到离子存在的影响。

This project aims to a microscopic understanding of water structure and relaxation dynamics at the solid/water interface. Our goal is to provide a molecular understanding on how the ordering and dynamics of interfacial water changes as function of the pH, namely of the surface protonation and charge state. As a further step we also aim to understand the role of different ions at the water solid interface. We will focus on a selected system, namely the CaF2/water interface for which a parallel simulation and experimental analysis will be conducted. In particular, we will perform ab initio simulations based on Density Functional Theory, while the experimental group of Dr. E. Backus at the Max Planck Institute for Polymer Research in Mainz will perform the SFG vibrational measurements.An innovative aspect here is the use of ab initio simulations to directly interpret the experiments at a molecular level. The first principles simulations are particularly suitable for modelling interfaces, since they naturally include polarization effects (including electronic polarization) which occur at a heterogeneous environment. In addition they can naturally include temperature effects and sampling of both enthalpic and entropic effects. Owing to recent progress in optimization of codes and the availability of supercomputing resources the time required for the simulations reduced drastically. Hence, the data acquisition in the experiments and simulation require a similar amount of time.The questions we would like to address include:(I) Solvent ordering, with particular emphasis on how far it extends and how it is influenced by the surface protonation state and surface charge density. What are the solvent vibrational properties at the interface and how they can be deduced from velocity-velocity (and surface specific) correlation functions?(II) The electrostatic potential at the interfaces. How does the potential depend on pH and how does it compare to experiments? (III) Description of the energy relaxation at the interface starting from localized vibrational excited normal modes.(IV) Influence of ions at the interface. In particular we would like to address how different ions (simple halides versus molecular ions) localize at the interface. How does an anion in direct proximity of the surface water molecule or an anion in the diffuse ion cloud influence the water ordering and modify the vibrational properties of water at the interface? In particular two prototype cases will be considered, namely Cl- and SO42-. Also in this case we will look at dynamics and energy relaxation. The key question here would be how the solvent energy relaxation is influenced by the presence of ions.