Effects of dielectric parameters. The dipole polarizability of an isolated particle α is an important parameter because it governs the relative sensitivity of a material's optical properties to the spatial arrangement of its nanoparticles. To appreciate why, consider that, within the p-truncation level of approximation, the particle permittivity ε p only appears in the governing equations via the dipole polarizability α (see, e.g., eq (9)-( )). As described in Methods, the induced particle polarization moments are determined by inverting a large matrix M (see eq (13)). The diagonal elements of M , which represent coupling between a particle and the incident field, contain multiplicative factors of α -1 while the off-diagonal elements, which represent coupling between two particles, are independent of α. Structural sensitivity of the optical properties is thus enhanced for more polarizable (i.e., higher |α|)