Hamiltonian of a water molecule bounded to a surface

Question

Where can I find a way to construct the hamiltonian of a water molecule bounded to a surface? More generally,how can one write the hamiltonian of an atom bounded to a surface?

Answer 1

There are lots of different models for water and its interactions, depending on what you want to do with them.

Here are some entry points:

• Simulation of water cluster assembly on a graphite surface
• Water Dynamics on the Surface of MCM-41
• Water–silica surface interactions

They either contain an explicit Hamiltonian or refer to one.

Answer 2

Arnold gave links to some publications about water adsorption on surfaces described with atomistic modeling. However, there are simples models, with simple hamiltonians, from which you can derive plenty of cool properties of adsorption of atoms on surfaces. (Here, I interpret your “bounded” as indicating physisorption; chemical bonds would be another topic altogether.)

• Langmuir model: the simplest, most effective. The Hamiltonian is defined as: 0 if the atom is not on the surface, $-\epsilon$ if it is. Divide your surface as an ensemble of $N$ possible adsorption sites, and treat using statistical physics in the grand-canonical ensemble ($\mu, V, T$). Enjoy!
• Possible improvements on Langmuir, such as the BET model, can describe multilayer adsorption.
• It is also possible to complement these models (either Langmuir or BET) by accounting for lateral interactions, i.e. interactions between molecules sitting on neighboring sites on the surface.

I hope you find these models interesting, as they describe a lot of the phenomenology of adsorption. I'd be happy to discuss follow-up questions!