Convergence of the DDA for ensembles of objects of irregular shape

The discrete dipole approximation (DDA) is commonly used to compute light-scattering properties of irregularly shaped particles. The DDA maps the particle into an array of cubic cells with side d < lambda. For a randomly oriented irregularly shaped particle, DDA has been shown accurate when kd|m| <= 1, where k is the wavenumber and m is the particle refractive index. We demonstrate that the DDA yields robust results even when kd|m| approximate to 1.2 when applied to ensembles of irregularly shaped dielectric particles and kd|m| approximate to 1.3 for conductive particles. This finding can greatly reduce the computational load required for performing such computations.