  We investigate whether microscopic cascading of second-order nonlinearities
of two molecules in the side-by-side configuration can lead to a third-order
molecular nonlinear-optical response that exceeds the fundamental limit. We
find that for large values of the second hyperpolarizability, the side-by-side
configuration has a cascading contribution that lowers the direct contribution.
However, we do find that there is a cascading contribution to the second
hyperpolarizability when there is no direct contribution. Thus, while cascading
can never lead to a larger nonlinear-optical response than for a single
molecule with the same number of electrons, it may provide design flexibility
in making large third-order susceptibility materials when the molecular second
hyperpolarizability vanishes
