Multispheres

Cluster of homogeneous spheres (well, almost like on the picture, but they have to be homogeneous) can be solved analytically in terms of infinite series. Such solution are based on Mie solution for individual spheres and subsequent expansion of these solutions to account for boundary conditions. Spheres can not intersect.

Name	Author	Type	Language	Description
GMM, GMM papers, GMM description	Xu	multispheres, Mie	Fortran	Codes which calculate (exactly) electromagnetic scattering by an aggregate of spheres in a single orientation or at an average over individual orientations (these codes were previously available on www.astro.ufl.edu/~xu/codes.htm). There are 3 files: code, description, and relevant papers.
Mackowski	Dan Mackowski	multisphere, Mie	Fortran	Codes for calculation of the scattering matrix and cross sections of neighboring, non-intersecting spheres. Dan Mackowski's papers on multisphere are one of the most comprehensive. Older local version.
MSTM http://eng.auburn.edu/users/dmckwski/scatcodes/	Dan Mackowski (2013)	multisphere, Mie	Fortran	MSTM (Multiple Sphere T Matrix) is a fortran-90 code for calculation of the electromagnetic scattering and absorption properties of a system of spherical surfaces. The code is designed to run either on serial platforms or distributed—memory compute clusters.