Capacitive density functional theory for structure and screening in ionic fluids and electric double layers with applications in sustainability

水的可持续处理和我们对能源的需求是我们在21世纪初面临的挑战。解决这些挑战的前景看好的技术利用了离子液体和双电层(EDL)的特性。当离子电解质和超电容(大表面)电极结合时，后者在电极-电解液界面上发展。EDL的物理特性对超容电极的大容量及其在能量采集、能量转换和去电离中的应用是至关重要的。在我们提议的项目中，我们将发展一种新的理论，以完善我们对电解液和EDL性质的知识。利用这个理论，我们将研究结构和静电屏蔽，它们不仅与建模和描述电解液和电容技术有关，而且还与化学(胶体)和生物学(离子通道，DNA)等相关领域有关。为了达到我们的目标，我们将应用经典的密度泛函理论(DFT)，这是统计物理中的一个微观框架。特别是，我们将(I)解决离子原始模型中长期存在的点状库仑电荷和空间硬核斥力的组合问题。这种新的方法对于描述EDL中的结构转变，从而理解EDL电极的异常电容是至关重要的。此外，我们将(Ii)开发一种新的方法来研究电解液中的显式溶剂以及在密度泛函理论中模拟有效的相互作用。基于这种理论方法，我们将研究离子水合作用和偶极溶剂分子的影响，它们被认为是描述最近在实验中报道的筛选长度莫名其妙的增加的关键成分。我们的研究将基于大量的数值计算。为此，我们将开发最先进的软件包CapDFT，并与公众分享。尽管如此，capDFT可以作为建模软件，特别是在应用科学中。与顶尖科学家的合作和参加会议将有助于传播我们的研究并改善我们的科学网络。

The sustainable treatment of water and our demand of energy are challenges that we are facing at the beginning of the 21st century. Promising technologies addressing these challenges exploit the properties of ionic fluids and electric double layers (EDLs). The latter develop at the electrode-electrolyte interface when ionic electrolytes and supercapacitive (large surface) electrodes are combined. The physics of EDLs is crucial for the large capacitance of supercapacitive electrodes and for their utilization in energy harvesting, energy conversion, and deionization. In our proposed project we will develop a new theory in order to complete our knowledge of the properties of electrolytes and EDLs. Using this theory we will study structure and electrostatic screening which are relevant, not only for modeling and describing electrolytes and capacitive technologies, but also for related areas like chemistry (colloids) and biology (ion channels, DNA). To reach our goal, we will apply classical density functional theory (DFT), which is a microscopic framework in statistical physics. In particular, we will (i) give a solution for the long-standing problem of combining point-like Coulombic charges and steric hard-core repulsions in the primitive model of ions. The new approach is crucial to describe structural transitions in EDLs and, consequently, to understand the resulting anomalous capacitance of EDL-based electrodes. Furthermore, we will (ii) develop a new approach for explicit solvents in electrolytes and for modeling effective interactions in DFT. Based on this theoretical approach, we will study ionic hydration and the effect of dipolar solvent molecules, which are assumed to be the key ingredients for the description of an unexplained increase in the screening length that has been reported in experiments recently. Our research will be based on extensive numerical calculations. To this end, we will develop the state-of-the-art software package capDFT, which we will share with the public. Though, capDFT can serve as modeling software, especially in the applied sciences. Collaborations with leading scientists and joining conferences will help to disseminate our research and improve our scientific network.