Instantaneous (spatial) mass density profiles for gold and water were computed separately with a spatial binning of width 0.25 Å (radial shells for AuNPs and rectangular blocks along the z-direction for the planar surface). At each time step, the coordinates of atoms were shifted so that the center of mass of the gold structure was at the origin. In the case of the planar surface, the profile was averaged over the positive and negative z-directions. The profiles for systems in the absence of heating were computed by averaging over the final 500 ps of the equilibration simulations, which were under NPT conditions at 300 K and 1 atm. For systems under heating, the steady-state profile was computed by time averaging the instantaneous profiles over the final 1 ns of each non-equilibrium steady-state simulation. The time averaged profiles were then further smoothed by applying a Gaussian filter with σ = 2 to generate the final equilibrium or steady-state profile.