The disordered fluid states are homogeneous and exhibit short-range structural correlations; the arrested states, while also globally disordered, appear more heterogeneous, and the local environments of some particles have a strong short-range (local crystalline) order. Optical properties from MPM. For each nanoparticle configuration obtained from the Brownian dynamics simulations, we perform optical simulations by solving Maxwell's equations for the electric field E(x, ω) in the geometry dictated by the particle positions x i .