  Electrochemistry experiments have established that the capacitance of
electrode-electrolyte interfaces is much larger for good metals such as gold
and platinum than for carbon-based materials. Despite the development of
elaborate electrode interaction potentials, to date molecular dynamics
simulations were not able to capture this effect. Here we show that changing
the width of the Gaussian charge distribution used to represent the atomic
charges in gold is an effective way to tune its metallicity. Larger Gaussian
widths lead to a capacitance of aqueous solutions (pure water and 1 molar NaCl)
in good agreement with recent ab initio molecular dynamics results. For pure
water, the increase in the capacitance is not accompanied with structural
changes, while in the presence of salt the Na$^+$ cations tend to adsorb
significantly on the surface. For a strongly metallic gold electrode, these
ions can even form inner sphere complexes on hollow sites of the surface.
