Numerical calculations with nite-dierence time-domain (FDTD) on metallic nanostructures in a broad optical
spectrum require an accurate approximation of the permittivity of dispersive materials. In this paper, we present
the algorithms behind B-CALM (Belgium-California Light Machine), an open-source 3D-FDTD solver operating
on Graphical Processing Units (GPUs) with multi-pole dispersion models. Our modied architecture shows a
reduction in computing times for multi-pole dispersion models. We benchmark B-CALM by computing the
absorption eciency of a metallic nanosphere on a broad spectral range with a six-poles Drude-Lorentz model
and compare it with Mie theory.