  In a previous paper
(http://www.phys.uri.edu/people/nightingale/publications.html, chem-ph/9406003)
we developed a form of variational trial wave function and applied it to van
der Waals clusters: five or less atoms of Ar and Ne modeled by the
Lennard-Jones potential. In addition, we tested the trial functions for a
hypothetical, light atom resembling Ne but with only half its mass. We did not
study atoms such as He with larger de Boer parameters, i.e., systems in which
the zero point energy plays a more important role relative to the potential
energy. This is the main purpose of the present paper. In fact, we study
clusters to the very limit where the zero-point energy destroys the ground
state as a bound state. A simple picture of this un-binding transition predicts
the power law with which the energy vanishes as the de Boer parameter
approaches its critical value and the power of the divergence of the the size
of the clusters in this limit. Our numerical results are in agreement with
these predictions.
