The AutoDock4 scoring function can be described as a classical (additive) force field supplemented with an implicit solvation model and a ligand entropy term. The force field consists of three terms: a 12-6 Lennard-Jones potential, a Coloumb potential with a distance-dependent dielectric constant, and a 12-10 potential for hydrogen bonds. The implicit solvation model is an additive pairwise potential in which the solvent accessibility of each atom is estimated based on the proximity of surrounding atoms . It is an empirical model that depends both on atom type parameters and the partial charges . It accounts for (de)solvation of both the ligand and the receptor. The ligand entropy term accounts for the loss of conformational freedom of the ligand upon binding, adding a penalty that is linearly dependent on the number of rotatable bonds.