Solution isn't converging

Hello everyone,

I'm having a problem with my simulation, where it isn't converging. It's a very thin plate (10 nm) of graphene, and the dimensions of it are around 0,5 um. I've made a simulation where the dimensions of the plate where about 10 um, and it converged correctly, but when I reduced it to 0,5 um, it isn't converging. There's another simulation where I choosed a 1 um dimensio, but I had to incresce the height of the plate to 50 nm. What I have to do to have a covergion.

The error mensage is "Failed to find a solution for the initial parameter.
Multigrid canceled.
Returned solution is not converged."

Thanks