(191f) Plasmonic Response of Nanoparticle Assemblies

The optical properties of materials composed of plasmonic nanoparticles can be tailored through the dielectric properties of individual nanoparticles as well as their spatial arrangement. By leveraging structure-dependent properties, self-assembly of plasmonic nanoparticles enables tunable optoelectronic, catalytic, and biomedical technologies. Understanding which material is optimal for a particular application is challenging because there is an enormous number of possible physical parameters and assembled structures to screen. Computational methods have the potential to accelerate this search, but current methods for determining the effective plasmonic properties require expensive numerical solutions to many-bodied systems of equations and are therefore limited to configurations of only a handful of particles, which are not representative of large-scale structural features and heterogeneities. In this work, we develop a mutual polarization method to rapidly simulate the optical response of nanoparticle materials, allowing for 10^3-10^5 nanoparticles to be probed at a time. The method is well-suited to configurations obtained from molecular simulations, enabling a complete computational framework that predicts both self-assembled structures and their optical properties. We use our mutual polarization method to investigate the plasmonic response of two important classes of nanoparticle assemblies: 1) random binary superlattices and 2) gels. Though these assemblies are impractical to investigate using conventional numerical approaches, the optical properties predicted from our mutual polarization method agree well with corresponding experimental measurements of lab-synthesized assemblies. Using the detailed information available in simulations, we elucidate the structural origins of the experimentally observed changes in optical behavior upon assembly. Our mutual polarization method is therefore a valuable tool for understanding the complicated structure-property relations governing plasmonic nanoparticles and will facilitate design of new optoelectronic materials.