Molecular Nanopolaritonics

加州大学洛杉矶分校的Daniel Neuhauser因开发了一种理解分子纳米极性的理论方法而获得了理论与计算化学项目的奖励。该项目旨在统一辐射和物质的处理方式，以便有效和准确地描述任意物理几何和电子结构的系统。在此研究之前，结合等离子体-物质的研究通常利用等离子体携带结构上的多极模式展开，虽然简单，但无法准确捕获任意几何形状或场奇点。另一方面，在整个系统中使用TDDFT在计算上是非常昂贵的。因此，从所使用的方法和测试这些方法所选择的应用程序的角度来看，PI是对以前的模拟的扩展。研究从fdtd类型的算法开始（将对近场应用进行修改），然后继续进行离散偶极子研究，最后使用流体动力张量DFT实现嵌入形式。分子部分采用实时TDDFT算法进行描述，并对其进行非线性处理，以捕捉系统的多谐波和混频特性。对更小尺度辐射特征的追求导致了等离子体动力学的新领域，在等离子体动力学中，光沿着金属纳米粒子阵列和波导的传输在小到几纳米（nm）的距离上进行研究。同时，电子结构的计算也达到了纳米尺度，因此辐射尺度和物质尺度的区别正在变得模糊。这导致了各种各样的研究，其中考虑了一些等离子体激子和激子的偶极发射耦合，具有有趣的共振，场和空间依赖性等等。纳米尺度的物质辐射（简称纳米极性电子学）现在已经成熟，可以对近场辐射和分子进行现实描述。PI和他的团队正在将麦克斯韦的近场描述与现代电子动力学研究相结合，以模拟纳米尺度上的物质-辐射（等离子体-激子，即极化子）组合系统。正在考虑的一些应用是：辐射传输的门控，特别是在具有双折射效应的大型等离子体系统中，包括关于分子是否可以控制这些系统的问题，可能用于成像的应用；纳米尺度上的非线性选择显微镜——一个对从工程到医学的传感应用具有潜在巨大影响的领域；将电磁近场能量转换为纳米尺度的物理运动，这在任何需要运动控制的领域都具有实际意义；在光伏电池中，等离子体有望减小吸收体的尺寸；近场和远场的匹配，这可能会受到分子运动的影响；等离子体逻辑电路的发展。

Daniel Neuhauser of UCLA is supported by an award from the Theoretical and Computational Chemistry program for work to develop a theoretical methodology to understand molecular nanopolaritonics. The project is intended to unify the treatment of radiation and matter in such a way as to efficiently and accurately describe systems of arbitrary physical geometry and electronic structure. Prior to this reseach, combined plasmon-matter studies typically utilized multipole mode expansions on the plasmon-carrying structure, which although simple, are unable to accurately capture arbitrary geometries or field singularities. Using TDDFT for the whole system, on the other hand, is prohibitively expensive computationally. The PI is, thus, extending previous simulations, both in terms of method used and applications chosen for testing those methods. The research starts with FDTD-type algorithms (to be modified for near-field applications), and continues on to discrete-dipole studies, and finally implements embedding formalisms using Hydrodynamic Tensor DFT. The molecular part is being described by a real-time TDDFT algorithm, and treated non-linearly as to capture the multiharmonic and frequency mixing characteristics of the system.The drive towards ever smaller scales for radiation features has led to the new field of plasmonics in which light transport along metal nanoparticle arrays and waveguides is studied at distances as small as a few nanometers (nm). At the same time, electronic structure calculations have also reached the nm size scale, so that the distinction between radiation and matter scale is being blurred out. This has led to a variety of studies where dipolar emission coupling of a few plasmons and excitons are considered, with interesting resonance, field- and spatial-dependence and more. Matter-radiation on the nanoscale (nanopolaritonics in short) is now ripe for a realistic description of both near-field radiation and molecules. The PI and his group are merging Maxwell's near-field description with modern studies of electronic dynamics, to simulate combined matter-radiation (plasmon-exciton, i.e., polariton) systems on the nanoscale. Some applications being considered are: gating of radiation transfer, specifically in large scale plasmonic systems with birefringence effects, including questions about whether molecules can control these systems, an application with possible use in imaging; nonlinear selective microscopy on the nanoscale -- a field with potentially huge impact for sensing applications from engineering to medicine; conversion of electromagnetic near-field energy to physical motion on the nanoscale, which will have practical importance in any field requiring motion control; photovoltaics where plasmons are hoped to reduce absorber sizes; matching of near and far fields, which could conceivably be affected by molecular motion; and the development of plasmon logic circuits .