The effects of charge transfer on aqueous and ionic systems

新奥尔良大学的Steven Rick和Sandia国家实验室的Susan Rempe得到了化学部化学理论、模型和计算方法项目的支持，他们开发离子和蛋白质链的电荷转移(CT)模型，建立在以前关于水的工作的基础上，并研究电荷转移对界面性质、水通过纳米通道的传输、离子溶剂化和生物离子通道的影响。两个经常对立的原则，效率的需要和精度的需要，指导着原子模拟相互作用势的发展。一种策略是使用量子力学计算或实验结果来确定重要的相互作用类型，然后开发有效的方法来处理这些相互作用。实验和理论研究表明，电荷转移在分子间相互作用中起着重要的作用。具体地说，对于接触的两个分子，两个分子之间的电子密度并不相等。因此，分子可以有很小的瞬时电荷，而离子可以有非整数电荷。这种数量的电荷转移可能对凝聚相系统的热力学和动力学有重要的和很大程度上未被研究的影响。还计划对非水体系中的离子进行研究，包括碳酸乙烯和离聚体。所有这些项目都涉及量子力学计算，包括CT模型的参数化和模型结果的验证。该奖项支持旨在开发和使用具有新水平的复杂程度的模拟模型的理论和计算研究，而不牺牲计算效率。计算机模拟的使用极大地提高了对分子水平上的材料的理解，这需要对粒子之间的相互作用进行数学描述。电荷转移是分子模拟中通常排除的一类相互作用，但量子理论计算表明这一点很重要。量子计算表明，电荷可以从中心分子或离子扩散到附近的粒子。例如，在水中，形式电荷为-1的氯离子与其邻居分享多余的电荷，其电荷减少约20%。这种离子和其他离子的电荷减少对环境非常敏感，因为它最近的邻居会改变，影响离子相互作用和通过各种材料的方式。这种电荷变化可能会对电解液的行为产生重要影响，例如，用于电池和水淡化过滤器的设计。这项工作将开发和使用电荷转移模型来研究各种材料中离子和水的结构和动力学，包括生物离子通道、净水膜和电池材料。

Steven Rick of the University of New Orleans and Susan Rempe of Sandia National Laboratory are supported by an award from the Chemical Theory, Models and Computational Methods program in the Chemistry Division to develop charge transfer (CT) models for ions and protein chains, building on previous work for water and to examine the effects of charge transfer on the properties of interfaces, water transport though nanochannels, ion solvation, and biological ion channels. Two often opposing principles, a need for efficiency and a need for accuracy, guide the development of interaction potentials for atomistic simulations. One strategy is to use quantum mechanical calculations or experimental results to determine the interaction types that are significant and then develop efficient methods for treating these interactions. Experimental and theoretical studies have demonstrated that charge transfer can play an important role in intermolecular interactions. Specifically, for two molecules in contact, the electron density is not equally shared between the two molecules. Thus, molecules can have small transient charges and ions can have non-integer charges. This amount of charge transfer may have important and largely unexamined effects on the thermodynamics and kinetics of condensed-phase systems. Studies of ions in non-aqueous systems, including ethylene carbonate and ionomers, are also planned. All these projects involve quantum mechanical calculations both to parameterize the CT models and to validate the results of the models.This award supports theoretical and computational research aimed to develop and use simulation models with a new level of sophistication, without sacrificing computational efficiency. The understanding of materials at the molecular level is greatly enhanced by the use of computer simulations, which require a mathematical description of the interactions between particles. Charge transfer is a class of interactions commonly excluded in molecular simulations but which quantum theoretical calculations indicate is important. The quantum calculations reveal that charge can be spread out from a central molecule or ion to nearby particles. As an example, in water a chloride ion, with a formal charge of minus one, shares this excess charge with its neighbors and has a charge that is reduced by about 20%. The charge reduction of this and other ions is strongly environmentally sensitive, as its nearest neighbors change, impacting how ions interact and flow through various materials. This charge variation could have important consequences on the behavior of electrolytes as, for example, used in batteries, and in design of water desalination filters. This work would develop and use charge transfer models for the study of the structure and dynamics of ions and water in a variety of materials, including biological ion channels, water purification membranes, and battery materials.