  The accurate and efficient computation of the electromagnetic response of
objects made from artificial materials is crucial for designing photonic
functionalities and interpreting experiments. Advanced fabrication techniques
can nowadays produce new materials as three-dimensional lattices of scattering
unit cells. Computing the response of objects of arbitrary shape made from such
materials is typically computationally prohibitive unless an effective
homogeneous medium approximates the discrete material. In here, we introduce a
homogenization method based on the effective T-matrix. Such a matrix captures
the exact response of the discrete material, is determined by the T-matrix of
the isolated unit cell and the material lattice vectors, and is free of spatial
dispersion. The truncation of the effective T-matrix to dipolar order
determines the common bi-anisotropic constitutive relations. When combined with
quantum-chemical and Maxwell solvers, the method allows one to compute the
response of arbitrarily-shaped volumetric patchworks of structured molecular
materials and metamaterials.
