How to Calulate the Scattering Cross-section of Au Nano Dimers?

Hello all,

I'm trying to calculate the scattering cross-section and the absortion cross-section of  Au Nanoparticle Dimer (two NPs side by side of R=50nm), with a gap of 8nm, in Comsol Multiphysics.

Now, I know how to calculate the scattering cross-section and the absorption cross-section of a single spherical Nanoparticle in Comsol. For a single nanoparticle the Power-flow outwards of the Nanoparticle surface is integrated. e.g.

nrelPoav = nx*emw.relPoavx + ny*emw.relPoavy + nz*emw.relPoavz;

(intop_surf(nrelPoav)/S_in)/sigma_geom

where,

intop_surf integrates over the surface of a single Nanoparticle. and sigma_geom is the geometric cross-section. and S_in = E0^2/(2*Z0_const)

Now, my question is when calculating the Scatering Cross section of two NanoParticles (Dimer) should I integrate over both the NP surface in a similar manner, or what should be my approach to calculate???

Thanks a lot.