Fig. 5. Flat configuration. Relative changes in the charge density in comparison to the zero bias, Δρ_V,0 = ρ_V – ρ₀ for (a) V = +1.5 V and (b) V = –1.5 V (isosurface values = ±8.1 × 10^–4 e per ų). Insets show an xy-sectional plane taken at the water molecule center of mass. (c) Charge density fluctuation at positive and negative applied biases, i.e. ΣΔρ = Δρ_1.5,0 + Δρ_–1.5,0 (isosurface value = ±5.4 × 10^–5 e per ų). In all of the cases, red (blue) indicates an excess (deficiency) of electrons. (d) Laterally averaged difference in the charge density in comparison to the zero bias: black for +1.5 V and red for –1.5 V; the water–metal system indicates the position of the atoms.