This program (MATLAB CODE) uses approximations and interpolation methods in order to describe Mie Scattering of a nanoparticle at an interface. Further, I compared the results to FDTD results (if you are intered in these results, just let me know).
Cross-sections and EM fields can be calculated (for the scattering on a nanoparticle with and without an interface)
A full program and theory description is included in this file.