Constant charge and fixed potential molecular dynamics was demonstrated for an explicitly solvated Au(111) surface. The simulated system consists of a 3x4x4 Au(111) surface slab and 32 deuterated water. The simulations were started from a previously obtained preequilibrated structure. Using the SCMVD model 8 Å of implicit water was added on top of the explicit water, and only the Γ-point was considered. The standard dzp-LCAO basis set was employed to present single-electron orbitals and density. The system was sampled at 330K using canonical Langevin dynamics as implemented in ASE. A time step of 1fs and a friction coefficient of 5ps -1 were used following the recommendations from our previous publication. The electrode potential was referenced against the inner potential of the uncharged interface i.e. the potential of zero charge (PZC) through computing the inner potential within the two central layers of gold as show in Figure (see also Supporting Information Section S2). The system was kept neutral by placing an SJM counter charge in the implicit solvent part, see Figure . As a model system for outer-sphere reactions, we considered a prototypical outer-sphere redox couple, Ru[NH 3 ] 3+ 6 . The entire simulation system, shown in Figure , consists of a Ru[NH 3 ] 3+ 6 near a five-layer thick slab of a Au(111) surface with a 5 × 5 surface cell. A 2×2×1 k-point mesh was used. The correct oxidation state (3+) on Ru[NH 3 ] 3+ 6 was enforced by using the recent grand canonical ensemble constrained DFT (GCE-cDFT) method at all fixed electrode potentials. GCE-cDFT applies a spatially localized external potential to obtain an a priori chosen distribution of charges in the simulation cell, see Supplementary Section S4 for more discussion. The electrode potential was computed from the inner potential within the central three inner gold layers. These inner potentials were then converted to an experimental SHE scale using Au(111)'s PZC at 0.52 V vs. SHE as detailed in the Supplementary Information Section S2.