We performed an ab initio study of molecular-doped periodic assemblies of ligand-stabilized Au nanoparticles. We found that the most stable dopant positions are near the nanoparticle surfaces, away from the center of interstitial positions. The dopants provide an effective screening mechanism, strongly reducing the nanoparticles charging energies. We also found a linear dependence of the Fermi level with dopant concentration, consistent with recent experiments, up to a critical concentration. For larger concentrations, a new regime is predicted. These features are well reproduced by a simple, analytical model for the material.