All,

I'm calculating some adsorption isotherms using a polymer as the framework. I wanted to block sorption in any inaccessible pores so after creating an isosurface I used the segregates tool in the volume visualisation toolbar to display only the visible pores. When I set up the sorption calculation I then selected the 'add new sorbates to the visible field regions' on the constraints tab. However, when I compare the isotherm the loading are higher for the constrained isotherm than they are for the unconstrained one (i.e. inaccessible pores are not blocked). Logically this doesn't seem to make any sense, if there is a greater volume to adsorb into in the unconstrained simulation then the loadings for the unconstrained isotherm should be higher than for the constrained one.

This got me wondering about the algorithm used in the simulations. I'm using metropolis and it is my understanding that this method will attempt to add sorbate molecules to any point in the box, if this point overlaps with the framework atoms, or, where the above constraint is applied, it is outside of the visible region then the attempted insetion is rejected. Is this correct? It occured to me that we could be constraining to regions that are more favourable to adsorption which would lead to more favourable energies and hence higher loadings but I'm not sure if this is the case.

Can anyone explain in greater detail how the constraint is applied and how this would affect loading?