[Towhee-users] IAST assumptions

Dear towhee users,

a little bit off topic but still:

What are the underlying assumptions (on a molecular level) of the  
Ideal Adsorption Solution (IAS) theory introduced by Myers and  
Prausnitz in 1965?

While there is usually no disagreement on the following assumptions,
- equal accessibility of all adsorption sites to all adsorbates
- reversibility of adsorption
- perfect mixing

I found two different statements about adsorbate-adsorbate interactions:
(1) They are assumed to be equal for all adsorbates (A<->A = A<->B = B<->B)
(2) They are assumed to be equal to zero.

What is the correct assumption? Do you know of any references?

Best regards,
Niels