Plasmonic response of complex nanoparticle assemblies

Optical properties of nanoparticle assemblies reflect the distinctive characteristics of their building blocks and their spatial organization, giving rise to emergent phenomena. Design of functional assemblies like clusters and superlattices has progressed through integrated experimental and computational studies establishing principles connecting structure to properties. However, conventional electromagnetic simulation methods are computationally expensive and inadequate for treating more complex assemblies, such as gels and mixed superlattices, hindering understanding and design. Here we establish a fast, materials agnostic method to simulate the optical response of large nanoparticle assemblies incorporating both structural and compositional complexity. This many-bodied, mutual polarization method resolves limitations of established approaches, achieving rapid convergence to accurate predictions even for configurations including thousands of nanoparticles, some touching or overlapping. The strategy naturally accommodates up to triply periodic boundary conditions. We demonstrate these capabilities by reproducing experimental trends and uncovering mechanisms governing the optical responses in assemblies of plasmonic semiconductor nanocrystals. Structurally complex gel networks and compositionally complex mixed binary superlattices with heterogeneity across length scales highlight the elucidation of both far- and near-field effects. This broadly applicable framework will facilitate design of more complex, hierarchically structured, and even dynamic assemblies for desired optical characteristics.