text: For experimental setups of chemisorption, the amount of adsorption of a particular system is quantified by a sticking probability value.
  However, chemisorption is very difficult to theorize.  A multidimensional potential energy surface (PES) derived from effective medium theory is used to describe the effect of the surface on absorption, but only certain parts of it are used depending on what is to be studied.  A simple example of a PES, which takes the total of the energy as a function of location:
  where  is the energy eigenvalue of the Schrödinger equation for the electronic degrees of freedom and  is the ion interactions.  This expression is without translational energy, rotational energy, vibrational excitations, and other such considerations.
  There exist several models to describe surface reactions: the Langmuir–Hinshelwood mechanism in which both reacting species are adsorbed, and the Eley–Rideal mechanism in which one is adsorbed and the other reacts with it.
  Real systems have many irregularities, making theoretical calculations more difficult:
  * Solid surfaces are not necessarily at equilibrium.  
  * They may be perturbed and irregular, defects and such.  
  * Distribution of adsorption energies and odd adsorption sites.  
  * Bonds formed between the adsorbates.
  Compared to physisorption where adsorbates are simply sitting on the surface, the adsorbates can change the surface, along with its structure.  The structure can go through relaxation, where the first few layers change interplanar distances without changing the surface structure, or reconstruction where the surface structure is changed. A direct transition from physisorption to chemisorption has been observed by attaching a CO molecule to the tip of an atomic force microscope and measuring its interaction with a single iron atom.
  For example, oxygen can form very strong bonds (~4 eV) with metals, such as Cu(110).  This comes with the breaking apart of surface bonds in forming surface-adsorbate bonds.  A large restructuring occurs by missing row.