By simulation of nanoantennas need to take into account a quantum capacity, a kinetic inductance, plasmons, a quantum conductivity, etc. What electromagnetics simulators allow you to do this (HFSS, CST, etc.)?
I dont see a priory a need to to use all those aspects mentioned in the question.
Normal scaling works well at least to the end of the optical frequency range (0.3 micron wavelength).What ever "nano" means in this context, forget all those "buzzwords" like plasmon etc and just do a normal EM simulation (of course taking into account the frequency dependent material parameters and keeping in mind that copper at optical frequencies is close to a bad dielectric.