Hi Steve,
As with other users of yukawa/colloid potential, I was also looking for a reference I could cite. I found the exact functional form in Samuel A. Safran's book, "Statistical Thermodynamics of Surfaces, Interfaces, And Membrane" where he discusses colloid interactions with respect to DLVO theory. I hope this information may help those who have questions about the functional form used for yukawa/colloid interactions in LAMMPS.
-Thanks,
Anand.