In this work we present the results of molecular dynamics simulations of the electrical double layer (edl) of a metal I electrolyte solution (Hg / 1.0 M KCl) interface at three different values of the electrical charge density. Ab initio derived interaction potentials are used. The image charges were taken into account using a fast multipole method (FMM) modification adapted specially to the geometry of the system. The results for the behavior of ions, water molecules and for the potential drop are compared to those obtained via other MD simulations of metal I electrolyte systems as well as to some experimental data for the system investigated.