Figure 1.

Concept of induced charge and image potential on an Au {1 1 1} surface as example (a) in vacuum and (b) in contact with a peptide solution. (a) In vacuum, a point charge +q causes opposite charges to enter through the ground and locate at the surface of the metal (pink negative charges) to generate an electrical field opposite to that created by +q. The image potential can be calculated assuming a classical image charge −q [16,19]. Positions of the jellium edge (broken line) and of the image plane (solid line) are shown. (b) In contact with a peptide solution, we find a dense collection of multi-poles which is overall charge-neutral but typically of non-zero dipole moment on time average. The electrons in the metal rearrange similarly at the surface to counterbalance the local electric field at the solution interface (grounding is not required). The image potential can be computed on the assumption of a mirror image of the collection of all atomic charges (shaded in pink). δ_V and δ_I represent system-dependent small offsets between the image plane and the jellium edge in vacuum and in the condensed phase. z_Sol and z_Sf represent the average position of the first atomic layer of the solution and of the metal at the interface. The arithmetic mean (‘interface edge’) characterizes the position of the image plane which maps the first atomic layer of the solution onto the first atomic layer of the metal.