Guilin Sun
Ansys Employee

Comparing results with others is very challenge, as there are many factors that the customers cannot control.  I have listed some reference papers in that post so you can see that some difference indeed exists, if all the geomery and material parameters are identical. We could not comment on any 3rd party tool, but we are confident with Lumericla FDTD as there are countless publications and experimental verifications, as well as commercial products designed by it. Since the gap is only 20nm and the diameter is only 139nm, it might be challenge to mesh them neatly, as they do not have a small, common factor to have integer number of meshes. In addition, the conformal variant 1 needs small-enough mesh however we do know how fine the mesh should be when it is small enough. please refer https://optics.ansys.com/hc/en-us/articles/360034382614-Selecting-the-best-mesh-refinement-option-in-the-FDTD-simulation-object