In the source, the design is that you have a framework, and at most two types of molecules: adsorbates and cations. Adsorbates are usually fluctuation in an adsorption simulations, and you would use the cation-type for molecules that are fixed in number.
So you could leave out the framework, and you're simulating a fluid. They are still called adsorbates, although they are strictly not. it is just a naming for different types of molecules.
The main reason is that the energy-decompositions is based on these types. So, you would also get the evaregs adsorbate-adsorbate, cation-cation, and adsorbate-cation energies.
