发展半经典分子动力学框架下的二维光谱理论以解析盐溶液中离子团簇化机理

Whether electrolytes exist as free ions or clusters in aqueous solution is an important issue which is widespread attention and controversial. It has been considered as a key issue for understanding many important problems. Ultrafast two-dimensional (2D) techniques is crucial for detecting ion cluster structures and its related dynamical process. This proposal aims to develop a set of semi-classical molecular dynamics theory that contains the feedback of the quantum system on the classical environment. It will combine with 2D spectrum calculation theory for understanding the microscopic mechanism of the ion clustering process. We will bring out the 2D spectrum calculation of specific experimental system by combining with exciton model, Numerical Integral of Schrodinger Equation (NISE) method and including the feedback of the quantum system on the classical environment.We will get some 2D spectrum signals that could be quantitatively compared with experimental 2D spectrum through the establishment of a few reasonable microscopic models, for revealing the microscopic mechanism of the ion clusters's existing or not, concentration and structure as well as the essence of the interactions between ions. This proposal will provide theoretical basis and guidance for experiments and application studies such as protein denaturation by salts and ion concentration dependent properties of ion channels that based on ion clustering.

电解质在水溶液中是以自由离子形式存在还是形成离子团簇是受到广泛关注且备受争议的一个课题，而它是理解许多重要问题的关键。二维光谱技术是探测离子团簇化结构及其相关动力学过程的重要研究手段。本项目旨在通过发展一套包含发色团对环境的反馈作用的半经典分子动力学理论结合二维光谱理论计算方法研究水溶液中离子团簇化过程的微观机理。我们将结合激子模型和薛定谔方程数值积分(NISE)方法，并引入发色基团对环境的反馈作用来实现具体实验体系的二维光谱计算。通过建立一些合理的微观模型，得到与实验可以定量对比的二维光谱信号，从而揭示影响离子团簇的存在与否、浓度和结构的微观机理以及形成离子团簇的离子间作用本质，为理解基于离子团簇化的蛋白质变性以及离子通道等实验和应用研究提供理论依据和指导。

本项目围绕盐溶液中离子团簇化的微观机理进行了一系列的理论研究，取得的主要进展如下：.（1）在理论方法发展方面，我们提出了一套将布朗振子相关函数分解为双指数函数形式的方案，并且还提出了只包含单指数项的两种变形方案。这些方案的精度都是可控的，并且适用范围广泛。实验上通常用两个或者很少项的指数函数来分析动力学结果，因此这个方案可以用来解释实验动力学的内在物理涵义。此外，我们还提出了一个一般的福克普朗克量子主方程，这是一种量子半经典理论，包含了Caldeira–Leggett’s主方程中缺失的三项“刻蚀”耗散项。这种对传统量子经典主方程的改进是简单而漂亮的，它极其显著地扩大了适用范围。这项工作将极大的有利于半经典理论应用于严格方法无法解决的复杂实际体系。.（2）在数值计算程序方面，我们将以上发展的理论数值程序化，使之用于各种待测体系。.（3）在盐溶液中离子团簇化的微观机理研究方面，我们搭建了合理的模型。在后续工作中，我们将继续应用发展的高效的半经典理论计算体系的动力学性质，分析团簇形成的微观机理。