The calibration of local chemical bonding at organo/metallic interface is a key component in large-scale molecular simulations for the self-assembly of organic molecules on metal surfaces, such as in molecular electronic devices, nanoparticle stabilization by passivated organic molecules and many other scientific issues in nanotechnology. We have constructed a group of classical potentials based on ab initio density functional theory (DFT) calculations to describe the chemical bonding between benzenedithiolate (BDT) molecule and gold clusters, including bond stretching, bond angle bending and dihedral angle torsion involved at the interface between the molecule and gold clusters. We have found that the bonding energy between Au and S can vary from 12.5 kcal/mol for a Au mono-atomic chain configuration to 51.3kcal/mol for a triangle Au cluster. Angle bending and torsion energy barriers seem remain the same as those for the BDT-Au and BDT-2Au complexes. The change in bonding energy, however, does not have significant impact on the global packing structure of BDT molecules on Au (111) surface. The Mulliken charge redistribution at the bonding interface (i.e., among bonded atoms) also does not show impact on the global packing structure, indicating that the dominant contribution for the self-assembly is from the intermolecular interactions, which includes the distant stable charge electrostatic and van der Waals interactions.