  Quasi-chemical theory applied to ion hydration combines statistical
mechanical theory, electronic structure calculations, and molecular simulation,
disciplines which are individually subjects for specialized professional
attention. Because it combines activities which are themselves non-trivial,
quasi-chemical theory is typically viewed with surprise. Nevertheless, it
provides a fully-considered framework for analysis of ion hydration.
Furthermore, the initial calculations are indeed simple, successful, and
provide new information to long-standing experimental activities such as
neutron diffraction by hydrated ions. Here we review quasi-chemical theory in
the context of a challenging application, Rb+(aq).
