Topics related to Lumerical and more

CHARGE convergence error

    • Handon Um

      I set up a silicon nanowire structure containing constant n-type doping and radial p-type doping.

      The dark current is 0 when the optical generation rate is disabled, despite the surface combination.

      Then I enabled the optical generation rate to get the photocurrent, but errors occurred like below.

      I think there might be something wrong with my CHARGE but I couldn't find it.


      My CHARGE including lsf file:

    • Niki Papachristou
      Ansys Employee

      Hello Handon,

      Like the message suggests the issue is most likely related to the mesh. I recommend:
      First identifying the smallest feature sizes in your design. This could be the thickness of a thin layer, the step between two geometries, or a curved object. You can use the ruler in the UI to find the value (e.g. 5 nm).
      Second, check your global mesh settings in the solver and any local mesh constraints to see if the specified values are small enough to resolve the smallest feature size. In the solver settings the minimum edge length is usually the most relevant setting.
      If the values are set according to the previous steps, you can proceed to mesh the structure and then visualize the mesh to confirm the smaller features are actually meshed properly. In some cases the "max refine steps" need to be increased to allow for the mesh to get closer to the set "min edge length".
      In many cases adjusting the mesh settings can resolve issues similar to what you have mentioned.




      • Handon Um

        Thanks for the specific reply, Niki.

        I'm adjusting the mesh settings you mentioned.

        Additionally, I want to ask one more thing.

        My CHARGE has no problem when I disable the optical generation rate.

        I can easily get the dark current result after running the simulation

        However, when I enable the optical generation rate, it requires more simulation time, and occurs convergence error.

        Is the .mat file that imported into my CHARGE can be one of the reasons for the error?


        I ran the FDTD simulation with mesh accuracy = 1 to obtain less data. 

        Should I check other settings related to FDTD?

    • Niki Papachristou
      Ansys Employee

      Hi Handon,

      For the convergence error, I would suggest evaluating the mesh size compared to your structure's smallest feature size, and also check if you can reduce the size of this 3D simulation. It is important that the minimum specified mesh size (set globally through the solver or locally through mesh constraint object) is smaller than the smallest features in your design (for example the space between two objects or thickness of a small layer).

      Kind Regards,


Viewing 2 reply threads
  • You must be logged in to reply to this topic.