  A Geant4-based Monte Carlo package named G4DS has been developed to simulate
the response of DarkSide-50, an experiment operating since 2013 at LNGS,
designed to detect WIMP interactions in liquid argon. In the process of WIMP
searches, DarkSide-50 has achieved two fundamental milestones: the rejection of
electron recoil background with a power of ~10^7, using the pulse shape
discrimination technique, and the measurement of the residual 39Ar
contamination in underground argon, ~3 orders of magnitude lower with respect
to atmospheric argon. These results rely on the accurate simulation of the
detector response to the liquid argon scintillation, its ionization, and
electron-ion recombination processes. This work provides a complete overview of
the DarkSide Monte Carlo and of its performance, with a particular focus on
PARIS, the custom-made liquid argon response model.
