Daniel Neuhauser of UCLA is supported by an award from the Chemical Theory, Models and Computational Methods program for work to develop a theoretical methodology to explore molecular nanopolaritonics with a large number of molecules. Molecular Nanopolaritonics intends to unify the treatment of radiation and matter on the nano scale. A previous award on this subject has introduced the concept of a unified treatment of matter and radiation on the nanoscale with arbitrary geometries and predicted that molecules will have large designed responses which can manipulate at will the transport of radiation in plasmon carrying structures. The present research unifies molecular and electromagnetic treatments on a larger scale through the development of theories that handle multitude of molecules with explicit time-dependent treatments and study the interaction with, and effects of, molecules and electromagnetic plasmons. The proposal tackles the difficult problem of embedding molecules directly on top of plasmon carrying structures, necessitating the development of multi-scale approaches that employ a detailed time-dependent orbital or density-matrix treatments in an inner region, supplemented by orbital-free or Maxwell studies on outer scales. The approaches use a time-dependent analogue of complex-Poisson descriptions, thereby significantly increasing the time-step of FDTD and making it commensurate with that of electronic dynamics. Further, new embedding techniques allow for designed orbital-free descriptions of plasmonics structures with the correct frequency response, thereby allowing large-scale embedding.
There are two disparate phenomena associated with radiation on the small scale. Metal structures support propagating plasmons, and molecules, whether few separate ones or large clusters, interact by dipole-induced fields. Nanopolaritonics is a recent name for the field which aims to unify the treatment. A well known direction is the effect on the molecules due to the interaction with the strong fields generated by the metal plasmons (which can be magnified by orders of magnitude in specific geometries, especially involving corners). However, Nanopolaritonics also includes the equally important and little-explored other direction, whereby molecules influence the propagation of plasmon waves. The PI with his group have shown in simulations that the effects are strong in both directions. At present they develop embedding approaches whereby adsorbed molecules are described quantum mechanically as well as the underlying adsorbing structure. Bigger regions are described by more approximate methods, such as orbital-free methods or Maxwell treatments, modified to concentrate on small scales. Applications of the methodology will be plenty: gating of plasmonics transport, sensing of individual molecules individually and through their effects on plasmons, non-linear phenomena and their effects on localized radiation transfer and absorption by adsorbed molecules. The most important feature is that this research unifies the two disparate fields of radiation and electronic dynamics, which taken together with realistic treatments, can exhibit novel physical features beyond perturbative or model-type treatments.