Metal oxide/water interfaces play a crucial role in many electrochemical and photocatalytic processes, such as photoelectrochemical water splitting, the creation of fuel from sunlight, and electrochemical $\mathrm{C}{\mathrm{O}}_2$ reduction. First-principles electronic structure calculations can reveal unique insights into these processes, such as the role of the alignment of the oxide electronic energy levels with those of liquid water. An essential prerequisite for the success of such calculations is the ability to predict accurate structural models of these interfaces, which in turn requires careful experimental validation. Here we report a general, quantitative validation protocol for first-principles molecular dynamics simulations of oxide/aqueous interfaces. The approach makes direct comparisons of interfacial x-ray reflectivity (XR) signals from experimental measurements and those obtained from ab initio simulations with semilocal and van der Waals functionals. The protocol is demonstrated here for the case of the ${\mathrm{Al}}_2{\mathrm{O}}_3\left(001\right)$/water interface, one of the simplest oxide/water interfaces. We discuss the technical requirements needed for validation, including the choice of the density functional, the simulation cell size, and the optimal choice of the thermodynamic ensemble. Our results establish a general paradigm for the validation of structural models and interactions at solid/water interfaces derived from first-principles simulations. While there is qualitative agreement between the simulated structures and the experimental best-fit structure, direct comparisons of simulated and measured XR intensities show quantitative discrepancies that derive from both bulk regions (i.e., alumina and water) as well as the interfacial region, highlighting the need for accurate density functionals to properly describe interfacial interactions. Our results show that XR data are sensitive not only to the atomic structure (i.e., the atom locations) but also to the electron-density distributions in both the substrate and at the interface.

中文翻译：

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使用X射线反射率数据验证氧化物/水界面的第一性原理分子动力学计算

金属氧化物/水界面在许多电化学和光催化过程中起着至关重要的作用，例如光电化学水分解，由阳光产生燃料以及电化学 $\mathrm{C}{\mathrm{Ø}}_2$减少。第一性原理的电子结构计算可以揭示对这些过程的独特见解，例如氧化物电子能级与液态水的能级对齐的作用。此类计算成功的必要前提是能够预测这些接口的准确结构模型，而这又需要进行仔细的实验​​验证。在这里，我们为氧化物/水界面的第一性原理分子动力学模拟报告一个通用的定量验证方案。该方法直接比较了来自实验测量的界面x射线反射率（XR）信号和从具有半局部和范德华功能的从头算模拟中获得的信号。该协议在此处针对以下情况进行了演示${铝}_2{\mathrm{Ø}}_3（001）$/水界面，最简单的氧化物/水界面之一。我们讨论了验证所需的技术要求，包括密度函数的选择，模拟像元大小以及热力学集合的最佳选择。我们的研究结果建立了验证第一原理模拟得出的结构模型和固体/水界面相互作用的一般范例。尽管模拟结构和实验最佳拟合结构在质量上达成一致，但是对模拟XR和测量XR强度的直接比较显示出从整体区域（即氧化铝和水）以及界面区域产生的定量差异。需要精确的密度泛函来正确描述界面相互作用。