Diverging simulation

- June 16, 2022 at 4:53 am
  
  srijeeta
  Subscriber
  
  When I am trying to simulate a length higher than 30 micron in FDTD( to find the transmissivity in a length higher than 30 micron),I am getting a message that the simulation is diverging,what could be the possible reasons for this?
- June 16, 2022 at 5:33 pm
  
  Guilin Sun
  Ansys Employee
  
  The first step is to make sure it is necessay to simulate 30um long. If there is a material interface in 30um, then change all the boundary conditions to Metal, and see if it diverges.
  if it still diverges, then reduce dt factor and use PML again till it converges.
  if using Metal BCs does not diverge it is due to PML:
  if the device has higher diffraction orders, large diffraction angles, please use "Steep angle PML".
  if no, you may need to use more number of PML layers, and make sure the PML thickness is about half wavelength or more. Or you may need to move away the PML from material interfaces. Please use only mesh accuracy 2 for the test. if you have override mesh, make sure its aspect ratio is not more than 5; and it is not too fine and close to PML.
  
  More details can be found here https://forum-legacy.ansys.com/discussion/25566/ansys-insight-diverging-simulations

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