MM approaches use a force field which gives the energy of a system as a function of the atomic positions and are usually used by SAMPL participants to compute solvation free energies and log P values. Force fields can be fixed charge and additive, or polarizable , and typically include all atoms, though this need not always be the case. These approaches are usually applied by integrating the equations of motion to solve for the time evolution of the system. Force fields such as GAFF ,