surface charge density - RF module

Hello everyone,

I am a little bit confused and I would be grateful for your help regarding the calculation of surface charge density on a gold nanoparticle in glass in comsol (RF module). Here is how I get the surface charge density on the gold nano sphere surface (by using Gauss Law):

Rho = (d(emw.Ex,x)+d(emw.Ey,y)+d(emw.Ez,z))*n_glass^2

where, n_glass = 1.5, which is the refractive index of the glass.

Is this correct/best way to do this or is there any other/better way of getting the charge density?

My surface plot for this 'Rho' looks really coarse even though I have a really high resolution during Meshing.

ps: On the related note, could someone tell me how could I get the polarization charge distribution?

Any light on this topic would be much appreciated :)

Thanks in advance,