Tang Fujie, Shi Kefeng, Wu Xifan
Department of Physics, Temple University, Philadelphia, Pennsylvania 19122, USA.
J Chem Phys. 2023 Nov 7;159(17). doi: 10.1063/5.0167999.
X-ray absorption spectroscopy (XAS) is a powerful experimental tool to probe the local structure in materials with the core hole excitations. Here, the oxygen K-edge XAS spectra of the NaCl solution and pure water are computed by using a recently developed GW-Bethe-Salpeter equation approach, based on configurations modeled by path-integral molecular dynamics with the deep-learning technique. The neural network is trained on ab initio data obtained with strongly constrained and appropriately normed density functional theory. The observed changes in the XAS features of the NaCl solution, compared to those of pure water, are in good agreement between experimental and theoretical results. We provided detailed explanations for these spectral changes that occur when NaCl is solvated in pure water. Specifically, the presence of solvating ion pairs leads to localization of electron-hole excitons. Our theoretical XAS results support the theory that the effects of the solvating ions on the H-bond network are mainly confined within the first hydration shell of ions, however beyond the shell the arrangement of water molecules remains to be comparable to that observed in pure water.
X射线吸收光谱（XAS）是一种利用核心空穴激发来探测材料局部结构的强大实验工具。在此，基于采用深度学习技术的路径积分分子动力学所构建的构型，运用最近发展的GW-贝叶斯-萨尔皮特方程方法，计算了NaCl溶液和纯水的氧K边XAS光谱。神经网络是根据通过强约束且适当归一化的密度泛函理论获得的从头算数据进行训练的。与纯水相比，NaCl溶液XAS特征的观测变化在实验结果和理论结果之间具有良好的一致性。我们对NaCl溶解于纯水时发生的这些光谱变化给出了详细解释。具体而言，溶剂化离子对的存在导致电子-空穴激子的局域化。我们的理论XAS结果支持这样一种理论，即溶剂化离子对氢键网络的影响主要局限于离子的第一水合壳层内，然而在该壳层之外，水分子的排列仍与纯水中观测到的排列相当。
