Combining Wave Optics and Electrostatics in simulations

Hi all,

I'm an engineering student trying to model a localized surface plasmon resonance (LSPR) of a metal nano particle (using wave optics) in the influance of a external static electric field.

I tried to provide a static electric field through the wave optics module but I was unable to find a suitable solution.

Hence, I tried to model the system individually for the LSP and the static electric field, and obtain the superposition.
The LSP was modeled using wave optics and the the static electric field was obtained using the electrostatics module ( using two parallel plates providing them with a +ve and -ve potentials, and keeping the metal nano particle in the middle . In this, I have used charge conservation for the metal nano particle ).

My questions are,

1. Is this method of taking the superposition correct for small fields, or are there any physical theories that govern these types of scenarios?

2. Is there a possible way to combine both these physics in the same study ?

3. When combining the Electric fields, to obtain the Electric field at a point is the following equation correct?

E = sqrt { conj(es.Ex + ewfd.Ex)(es.Ex + ewfd.Ex) + conj(es.Ey + ewfd.Ey)(es.Ey + ewfd.Ey) + conj(es.Ez + ewfd.Ez)*(es.Ez + ewfd.Ez) }

I would really appreciate someone can please provide me an answer for my questions.

Thank you!