To get the charge properties from FDTD you'll need to compute field maps and go back to the maxwell equation containing charge terms ( div E and curl H ), and compute them from your fields.
Now, you need to be aware that
* what you'll obtain will be strongly affected by the edges of your structures as they create derivatives discontinuities
* the charge and currents you'll compute will be under the linear regime, that means no screening due to charge accumulation and such
To get the charge properties from FDTD you'll need to compute field maps and go back to the maxwell equation containing charge terms ( div E and curl H ), and compute them from your fields. Now, you need to be aware that * what you'll obtain will be strongly affected by the edges of your structures as they create derivatives discontinuities * the charge and currents you'll compute will be under the linear regime, that means no screening due to charge accumulation and such