Use the PM6-DH procedure of: Jan Rezac, Jindrich Fanfrlık, Dennis Salahub, and Pavel Hobza, "Semiempirical Quantum Chemical PM6 Method Augmented by Dispersion and H-Bonding Correction Terms Reliably Describes Various Types of Noncovalent Complexes", J. Chem. Theory Comput. May 2009. See: http://pubs.acs.org/doi/abs/10.1021/ct9000922
Normally, two or three calculations would be needed to get the binding energy.