Currently, AM1/CM1A-BCC models are widely employed to assign atomic partial charges and were reported to reach fair results on FEP benchmark sets. In this model, atomic charges are firstly determined using the Mulliken charges computed at semi-empirical level of theory (e.g., AM1 or CM1A). Then, they are further adjusted using bond charge correction (BCC), which is a correction only depends on the molecular topology. The BCC parameters are initially fitted to electrostatic potentials (ESP), and then refined to reproduce the experimental solvation free energies of some model molecules. Protein-ligand binding free energies, however, to the best of our knowledge, have not been used as a direct fitting target. The protein-ligand interaction involves many protein residues and ligand functional groups, thus are affected by a large number of parameters. Manually fine-tunning all these parameters simultaneously could be a difficult task, even for experienced experts with excellent intuitions.