# How to calculate the forces of attraction between a surface and molecules of a substance at a corrosion affection? [closed]

Previously, a question was asked about an equation that is able to calculate the forces of attraction between a surface and molecules (of another substance). During the discussion of the question a thought for a new question arose.

Let us suppose that a surface and molecules of another substance interact to each other. The substance is something like honey, clay, glue, or resin, i.e. one has an adhesion property. Besides, some of the substances can be corrosive in relation to the surface. (Undoubtedly, corrosive substances may not have an adhesion property as well.) Corrosion can affect in different ways that depends on its activity (strong/weak/medium etc.).

## Interesting questions appear.

Due to an action of corrosion an exchange of atoms between the surface and molecules of the substance can appear. Therefore the system will have moving cores of atoms and in this case the Hamiltonian of the cores of the atoms cannot be neglected. Is it right? Does Hartee–Fock and DFT theory allow taking into account moving cores of atoms? Maybe is there a phenomenological theory doing a calculation of attraction forces of the system without solving Hartree–Fock or Kohn–Sham equation? In the process of the interaction, hydrogen bonds can appear. How can they be taken into account?

• I think you need to narrow the scope of your question. It sounds like you are interested in understanding behavior at multiple length scales. But in principle, yes. If you have corrosion, you have to account for electrochemical reactions at the interface, which needs quantum mechanical treatment. If this is a metal or alloy, atoms from the surface are oxidized and dissolved into the adjacent phase. Modeling these processes ab initio is a current frontier for theoretical electrochemistry. Sep 28, 2022 at 15:37
• Do you want to calculate the attraction force, or the attraction energy, or the total interaction energy? There is no unique way to partition the total interaction force (or energy) into attraction and repulsion contributions, and the total interaction force must be zero when the system is at equilibrium (so it's not interesting). This means that the total interaction energy is what most people are really interested in, even if they intuitively think of the forces first. Moreover, the total interaction (Gibbs free) energy is directly related to the adsorption equilibrium constant. Oct 2, 2022 at 12:53
• @wzkchem5 Thanks for the note. Something that holds the substance to the surface. I guess it is the total interaction energy. Oct 3, 2022 at 6:05