Divergence due to radius of sphere

My simulation diverges for this simulation with sphere radius of 20nm. However, the simulation does not diverge at radius 10nm. Can someone please explain why this happens?

Blu Ray - particles periodically between ITO and ZnO.fsp (364.0 KB)

Dear @ssamiha

This can have multiple reasons. The best practice will be be to try few things as is described in details in this page:

https://kb.lumerical.com/en/index.html?layout_analysis_diverging_simulations.html

Please keep me updated with your findings.

Thanks