K. Chadan et R. Kobayashi, A SUFFICIENT CONDITION FOR THE EXISTENCE OF BOUND-STATES IN A POTENTIAL, Journal of mathematical physics, 38(10), 1997, pp. 4900-4908
For a wide class of purely attractive potentials, we obtain a new suff
icient condition for the existence of bound states for any angular mom
entum. Applied to some exactly soluble cases, the condition gives good
results as compared to exact results. (C) 1997 American Institute of
Physics.