NanoTD-Audit: Passivity and charge-consistency checks for local dispersive FDTD with separate HDM and QCM diagnostics
Description
Reliable time-domain nanoplasmonic calculations require separate verification of the dispersive material model, explicit field update, charge bookkeeping, electromagnetic normalization, boundary treatment and spatial refinement. We present NanoTD-Audit, a documented validation package for local Drude–Lorentz auxiliary-differential-equation finite-difference time-domain (ADE–FDTD) calculations, with separate component diagnostics for hard-wall hydrodynamic Drude-model (HDM) and quantum-corrected-model (QCM) extensions. The supplied three-dimensional solver implements the local-response branch only; it contains neither a finite-geometry hard-wall HDM update nor a QCM gap-current or coupled HDM–QCM nanogap solver. The package combines a nonnegative-residue gold fit, explicit Yee/ADE update and stability checks, a four-level local-Au sphere FDTD–Mie audit on one common physical configuration whose boundary sensitivity is independently checked at ℎ=12nm, acquisition-window and Courant studies, an operator-consistent Gauss-law audit, and a closed source-free, absorber-free bulk Yee/ADE energy audit. Over 480–820 nm, the finest ℎ=4.5nm sphere errors are 3.31%, 13.76% and 11.18% for extinction, absorption and scattering, respectively; scattering is already plateaued between 6 and 4.5 nm, so neither asymptotic convergence nor the proposed two-percent predictive gate is claimed. The literature QCM table is retained only as a geometry-integrated effective metric carrying the source-reported S/m label, not as an independently established three-dimensional pointwise constitutive conductivity. NanoTD-Audit is therefore a reproducible local-response verification tool with separate HDM and QCM diagnostics rather than a full nonlocal-tunnelling solver.