Core shell Au@Ag Extinction calculation

I am trying to simulate the extinction spectra for a core-shell Au@Ag nanoparticle. I have some problems maybe with the script i use or maybe with the simulation itself. My goal is to have a 15 nm diameter core of Au and to make some simulation on different shell diameter of Ag to see how the extinction spectra will modify.
Here is my simulationAu@Ag 1 nm.fsp (486.9 KB)
Also here is the script i use to calculate the extinction mie_analysis_3d.lsf (6.5 KB)
If anyone can look on my simulation and script, maybe i did something wrong.

I found out that using the Johson an Christy Au and Ag materials affected my extinction simulation, now i get the two normal peaks coming from the plasmonic hibridization, but the extinction is not even close with the experimental ones. The gold nanoparticle extinction in fdtd is exactly the same with the experimental one but when i add the Ag shell is too far from what i got experimentally

Dear @Bogdan.Man

Thank you for providing simulation files.

I checked your .fsp file and I had a few comments about it:

  • It looks like mesh override only includes the spheres. As is explained here, its a good practice to increase mesh override region to include the entire TFSF source region.

Note: Mesh override region
For simulations with metals, the mesh override region is often used to more accurately resolve the locations of the metal interface, especially with curved surfaces. In this simulation, the mesh override region is large enough to encompass not only the gold sphere, but also the entire TFSF region. This was done intentionally; the TFSF sources work best in uniformly meshed regions.

  • Also note that the mesh spacing of the override region effects the location of the analysis boxes. Sources require a certain amount of space to inject the fields. The amount of space required is ~2 mesh cells and is depicted graphically by light white shading that surrounds the source. Within this region, the fields are not physically meaningful. Hence monitors should not be placed in this region.

  • You have a high mesh aspect ratio in your simulation, close to PML boundaries. This can cause some artefacts and poor PML absorption as is explained here:
    This is due to very fine mesh used by mesh override. To solve the problem, start by coarser mesh in the mesh override
    region, and then use a higher mesh accuracy in the FDTD region. Make sure that aspect ratio never goes above 10.

  • You can learn more on how to calculate extinction cross section here to help you check your scripts. Also, a convergence test is required to make sure that the results are converging.

Please keep me updated if you had any follow up questions.

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