where the general nomenclature, E basis geometry (X), represents the electronic energy of species X (R for probe, (H 2 O) n for a water cluster of size n, and complex for the water cluster-probe aggregates), at the geometry specified by the subscript and using the basis set identified by the superscript. For example, the term E R Complex (R) represents the electronic energy of a probe at its geometry in a complex using the probe basis sets. Note that Equation 1 can be written alternatively as