and compositional complexity. This many-bodied, mutual polarization method resolves limitations of established approaches, achieving rapid, accurate convergence for configurations including thousands of nanoparticles, some overlapping. We demonstrate these capabilities by reproducing experimental trends and uncovering far-and near-field mechanisms governing the optical response of plasmonic semiconductor nanocrystal assemblies, including structurally complex gel networks and compositionally complex mixed binary superlattices. This broadly applicable framework will facilitate design of complex, hierarchically structured, and dynamic assemblies for desired optical characteristics.