DFTMD simulations of Au/NaCl(aq) under finite D To begin with, both Au(100)/NaCl(aq) and Au(111)/NaCl(aq) system (Figs. and) were well equilibrated with semi-classical MD simulations under the same electric boundary conditions before porting the system into DFTMD simulations (See Supporting Information for details). This has been shown to be very useful to speed up the convergence of capacitance calculations. The Helmholtz capacitance can be computed using the formula shown below (Eq. 1), similar to the one used in the case of insulting oxide with proton charge. However, a key distinction here is that DFTMD simulations have been carried out under finite D and the imposed surface charge (σ m = D/4π) is electronic (free) charge on the metal surface instead of adsorbed proton charge due to the acid-base chemistry at different pH values. 44