Molecular Nanopolaritonics

加州大学洛杉矶分校的Daniel Neuhauser得到了理论和计算化学计划的奖励，以表彰他在开发一种理解分子纳米极化子的理论方法方面所做的工作。该项目的目的是统一对辐射和物质的处理，以便有效和准确地描述任意物理几何和电子结构的系统。在这项研究之前，组合等离子体物质研究通常利用等离子体载流子结构上的多极模式展开，虽然简单，但不能准确地捕捉任意几何或场奇性。另一方面，为整个系统使用TDDFT的计算代价高得令人望而却步。因此，PI扩展了之前的模拟，无论是在使用的方法方面还是在测试这些方法所选择的应用方面。该研究从FDTD类型的算法(将针对近场应用进行修改)开始，然后继续到离散偶极子研究，最后利用流体动力张量DFT实现嵌入形式。分子部分由实时TDDFT算法描述，并进行非线性处理以捕捉系统的多次谐波和频率混频特性。辐射特性向更小的尺度发展导致了等离子体的新领域，在该领域中，光在小到几纳米(Nm)的距离内通过金属纳米粒子阵列和波导进行研究。与此同时，电子结构计算也达到了纳米尺度，使得辐射和物质尺度之间的区别正在变得模糊。这导致了各种研究，其中考虑了几个等离子体激子和激子的偶极发射耦合，具有有趣的共振、场和空间相关性等。纳米尺度上的物质辐射(简称纳米极化子)现在已经成熟，可以对近场辐射和分子进行真实的描述。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，在纳米尺度上模拟物质-辐射(等离子体激子-激子，即极化子)组合系统。正在考虑的一些应用包括：辐射传输的门控，特别是在具有双折射效应的大型等离子激元系统中，包括分子是否可以控制这些系统的问题，这是一个可能在成像方面的应用；纳米尺度的非线性选择显微镜--这是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，这将在任何需要运动控制的领域具有实际意义；光伏技术，其中等离子体激元有望减小吸收体的尺寸；近场和远场的匹配，可以想象到它会受到分子运动的影响；以及等离子激元逻辑电路的开发。

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 .