Well one has to decide whether to go with molecule-molecule, or bulk interactions... That'll dictate the symmetry... With mol-mol maybe you could approx as spherical and slap together some H-like wavefunctions, concentrate on isolated 2-body interaction, calculate overlap integral... I am all about approximating crap as spheres, haha...
I'd try a Lennard-Jones 6-12 potential function. I don't really think there is any angular dependence, and while the colatitude might have some small effect, I'd bet it's negligible.
Hmmmm... Yeah sure in the beginning you could talk about the Windex adsorbing onto the crud-surface and model it as W-C, two body surface formation, in some potential well, but at some point it becomes energetically favorable for crud to dissociate from surface bonded to W and take a repulsive route of some sort... Of course if you look at Windex-crud bonding orientation, the bond strengths are going to be all about angular dependence... I dig my napkin-back static coeff scenario better... Calculate rate and extent of dissolution, which won't be instantaneous and 100% as Windex would claim...