A discussion about the accurate computation of the total time-dependent (conduction plus displacement) current in quantum and classical devices is presented. In particular, two different methods for the practical computation of the total time-dependent current are compared. The first method computes the conduction and the displacement currents from the rate of particles crossing a particular surface and the time-dependent variations of the electric field there. The second method uses the Ramo-Shockley theorem to compute the total time-dependent current on that surface from the knowledge of the particle-trajectory dynamics in a 3D volume and the time-dependent variations of the electric field on the boundaries of that volume, As an example, we present the computation of the total tunneling time-dependent current in a Resonant Tunneling Diode. From a computational point of view, it is shown that both methods achieve local current conservation, but the second is preferred because it is free from "spurious" peaks. Finally, the second method is used to accurately show the viability of a 200GHz harmonic generation from 50 GHz input signal for a Driven Tunneling Device.
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