Incorrect Absorption/Scattering From Ag Sphere



I have been attempting to calculate the scattering and absorption spectra for a 75 nm diameter Ag sphere using FDTD-solutions. There must be an error in the way I am setting up my .fsp files (included below) because the spectra I get have strong oscillations/structure:

Absorption Cross Section:

Scattering Cross Section:

These oscillations are absent in the spectra I get using Mie theory (JC dielectric function for Ag used in both cases).

I’ve followed the suggestions given in previous posts to solve similar issues (e.g. How to set the parameters to simulate the scattering or absorption of a gold nanorod) but my problem has persisted. For example, I’ve ensured that the auto-shut-off is reached in the attached simulation, and have even lowered the shut-off to 1e-6. I’ve also varied the mesh size in the override region from 2.0 - 0.5 nm with little to no improvement observed.

Any comments/suggestions would be greatly appreciated.

75nm_Ag_sphere.fsp (391.4 KB)
75nm_Ag_sphere_p0.log (8.6 KB)


I guess the main issues here are likely the material data, and mesh. Simulation involving silver material, the real part of the index is very low in the visible range, can be quite challenging. This is discussed here. Oftentimes, it might be necessary to test the results with different types of mesh refinement options, and size.

I have done some quick tests for you, looks like now the results are closer to the theory. The main edit is conform 0 -> conformal 1. I have also done other minor edits like mesh size, anti/sym boundary conditions, but there are more just to speed up the simulation.

If you have follow up questions, please let us know.

Mie_script.lsf (618 Bytes)
75nm_Ag_sphere_KC.fsp (315.3 KB)