  We investigate the structure and stability of Bose-Einstein condensate of
$^{7}$Li atoms with realistic van der Waals interaction by using the potential
harmonic expansion method. Besides the known low-density metastable solution
with contact delta function interaction, we find a stable branch at a higher
density which corresponds to the formation of an atomic cluster. Comparison
with the results of non-local effective interaction is also presented. We
analyze the effect of trap size on the transition between the two branches of
solutions. We also compute the loss rate of a Bose condensate due to two- and
three-body collisions.
