I am quite confused with the multiphysics simulation of NEMS/ MEMS structure for optical or electromagnetics study. I'm using comsol multiphysics 5.5 version, the mechanical simulation results or deflection I'm getting with some voltages, but the thing is that the simulation is showing an error inside the air box, but it is fine without the airbox. Now I need to see the optical transmission/reflection spectrum after the deflection. The airbox is then a must for optical simulation to maintain structural similarity and port excitation. The problems are that:

1)Why inside the airbox is the mechanical simulation showing error even though I'm using moving mesh?

2) How to correctly import the deformed structure for optical simulation (as there are no multiphysics coupling with electromagnetics with mechanics ) after getting the deflection profile, as one paper example, NEMS-Based Infrared Metamaterial via Tuning Nanocantilevers Within Complementary Split Ring Resonators.

They have suppressed the simulation information, as most of the papers of the reputed journals.

Suppose on the deformation profile one have different capacitance value, one gets a different carrier density, one gets refractive index/ permittivity value at different locations.

But again how to get different capacitance values at different positions, as capacitance parameter variation in comsol I could find only for voltage.

The problem is (2) in general for any other ways. The problems are (1) & (2).

Any valuable suggestions would be very much helpful...