Journal of Statistical Physics, VoL 33, No. 2, 1983, p. 477-484.
We demonstrate how to construct a large class of interacting quantum systems for which an exact solution may be found for the ground state wave function and ground state energy for some range of interaction parameters. It is shown that the ground state exhibits singularities in these cases, and in some simple instances the exact ground state phase diagram and critical indices are also found.