Extinction cross-section from a hexagonally arranged array of metallic nanoparticles using TFSF source



I would like to calculate extinction cross-section from ‘infinite’ periodic array of metallic nanoparticles that are hexagonally arranged, while using a TFSF source that I have been using for single nanoparticle case.
I tried enclosing one particle in the array and using PBC or Bloch boundary conditions to obtain the extinction cross-section, but the result I get seems identical to the single nanoparticle case I have been doing, so I am not sure if I am doing it correctly. So I tried setting up the mesh in the way shown in the image, and of course I get a strange result. Could you please teach me how to set up the simulation correctly for this? I’ve included the .fsp file.

Thank you.

Sean Park

Hex_arranged_array_example.fsp (511.1 KB)



Typically one use the Bloch boundary condition if the angle incidence is not zero. For your system, you have to use either a periodic boundary condition for x & y. Alternatively, you can further minimise the calculation size with symmetry.

Here is a good article in the knowledge base about the use of boundary conditions.


Best Wishes,



For the hexagonal, also in normal incidence, you must calculate both polarizations



For periodic structures, we suggest using the regular plane wave source with periodic (or Bloch boundaries for angled incidence, as mentioned by @vivek). You only need to simulate one unit cell and measure transmission and reflection; for example, if you get that the transmission at a certain wavelength is 25% it means that the reflection cross section is 25% of the unit cell area. This is discussed here.